We live in a metal box on wheels, so weather becomes a demanding taskmaster we can never ignore.

This spring, we faced down the polar vortex and the bomb cyclone.

Over the past four-plus years, we’ve had to reroute for blizzards, tornadoes, hail, extreme heat, as well as forest fires, choking smoke and strong winds that would rock our high-profile vehicle.

Our trip from Arizona this spring to visit Tom’s sister in South Carolina put us in the path of deadly storms and freezing temperatures, and had the added joy of an unexpected failure of our diesel-exhaust system, triggering the “10 starts left” dash alert that strikes terror in a nomad’s heart.

Still, we persevered. We skirted around dropping thermometers and squall lines to walk across the Edmund Pettus Bridge in Selma, Alabama, and visit the National Memorial for Peace and Justice in Montgomery, which examines the legacy of slavery, lynching, segregation and injustice. On the way back, we went to a sea-turtle hospital on Jekyll Island in Georgia, Jimmy Carter’s childhood home and his train-depot headquarters in Plains, visited old-growth cypress and tupelo in The Big Thicket in Texas and hiked an old rail line in Mississippi called the Tuxachanie Trail.

We’ve made the trip to South Carolina before, and each time we try to take a different path, once going south to Big Bend National Park and skirting along the Gulf coast. This time we planned to go farther north, but remnants of the polar vortex pushed freezing temperatures and us to a route farther south.

Freezing temperatures are a problem because we’re warm-weather freaks who plan to stay where it’s 72. Therefore, we don’t winterize our van.

Technical note, number one: (Probably more than you want to know, but fascinating if you live in a home on wheels.) To winterize, you drain your water tanks and pump pink RV antifreeze through your plumbing, which is mostly plastic piping. This means you don’t use the water system until you de-winterize by flushing out the pink stuff. Some RVs are built with some insulation of the piping system, but ours is not. Living in it and heating it at night with our propane furnace gives some slight protection, and the plumbing can withstand temperatures that dip slightly below 32 for a couple of hours, but anything more could cause problems.

Normally, we would wait a few weeks until spring had sprung a little more, but we had date-specific restrictions, and needed to be in South Carolina by February 26, just as the polar vortex was retreating. We stayed south, watching the predicted lows to find overnights stops in central Texas that didn’t drop below 30, and turned up our furnace.

Things in Greenville, South Carolina, were warm enough that our driveway surfing posed no problem for about a week, until the day we planned to leave. That night, temperatures were plunging into the low 20s. Time to get the heck out.

We had hoped to see the Little River Canyon National Preserve in Alabama, with a 700-foot gorge dubbed “The Grand Canyon of the East.” But it was too cold for comfort, so we rerouted to Jekyll Island, part of Georgia’s Golden Isles and, in the late nineteenth century, a private winter playground for the Morgans, Rockefellers and other one-percenters of the era. Today, it is a state park and houses a fascinating sea turtle center.

Next stop on the avoid-the-cold tour: Plains, Georgia, and Jimmy Carter’s home.

A planned series of rail-to-trail hikes was dumped for one hike on the Tuxachanie National Recreation Trail in Mississippi’s De Soto National Forest. The former spur of an Illinois Central line takes you past the site of an 1800s timber and turpentine operation, featuring cypress swamps and long-leaf pines.

Plans to revisit the Natchez Trace, site of a legendary, whole-family, pre-Epic Van road trip, were dropped with reports of a strong line of storms creating tornadoes. One touched down in Columbus, Georgia.

We ran farther south across Louisiana, grabbing a quick bag of boiled crawfish and some daiquiris from one of Louisiana’s crazy drive thrus and spent the night at a Walmart. Next, we headed to southeast Texas to hike The Big Thicket, where we saw old-growth cypress, slumbering snakes, snails and Tupelo trees.

It seemed like smooth sailing toward the Hill Country, and we thought we’d camp for a few nights at the Hill Country State Natural Area, until the ranger told us they were expecting quarter-size hail the next night. Our rooftop solar panels are supposed to withstand nickel-sized hail, but I wouldn’t want to test it, and flying balls of ice have made me skittish since friends told us how their truck windows were blown out in a hailstorm near Mount Rushmore one year.

So back on the road. The weather service and media were issuing dire warnings of a winter cyclone bomb. The weather apps on my phone, which track increasing severity of storms with yellow to orange to red, looked like a bloody knife slicing across the entire U.S., an open wound between us and home.

We had to find a safe place to sleep, so we headed south, toward Uvalde, Texas, and a Walmart Supercenter open 24 hours. That way, in case of tornado, we could run inside. And, presumably, it would have a gas station with a metal awning we could park under if it hailed.

Then it happened: A check DEF fluid alert on the dash, then the dreaded 10-starts left alert.

Technical note two: The Epic Van has a diesel engine. To mitigate environmental damage, owners must manually fill a tank under the hood with DEF, diesel exhaust fluid, deionized water that lowers nitrogen oxide in the exhaust. This isn’t just because we’re nice and care about cleaner air. It’s a federal requirement. So the exhaust system monitors compliance with three meters, one that senses when the DEF tank is empty, and two more “downstream” that monitor NOx emissions. If any meters are unhappy, the 10-starts alert comes on. After 10 starts, the vehicle goes into “limp” mode, meaning it won’t go more than five miles per hour. NOW, you get why it’s terrifying. When you’re seeking out the roads not taken, the remote campsite, or boondocking deep in a forest, 10 starts can add up fast. And we now know that 10 becomes a relative number, with the system sensing how many miles you’re driving, so a sprint toward home that lasts hours could mean 10 could drop to five, skipping entirely nine, eight, seven and six. Add to this the fact that not all Mercedes dealers service Sprinter vans, so repairs can be hundreds of miles away. We experienced this terror a couple years ago, when the 10-starts alert came on in Arkansas. We made it home and found that the fill sensor had malfunctioned and had to be replaced. This time, we called the Mercedes dealer in Boerne, Texas, near San Antonio, which could look at the van if we could be there at 7:30 a.m. We took it.

We drove on to Uvalde and parked, walking a mile to dinner because we didn’t want to use a valuable start.

If you read about our tornado scare in the central plains in 2015, you know the drill. Tom goes to sleep, snoring happily, as I stay up all night feverishly refreshing the weather map to watch the storm’s progress.

What had earlier seemed like a good margin of safety evaporated as the tail of the front continued to slip farther and farther south. I watched, and waited, and watched, and waited. Tornado alerts all along the front. Severe thunderstorms. Hail. The line kept dipping south, and slowing. It would arrive at midnight, then 1, then 3. Our county came under a tornado watch. We had to leave at 5:30 a.m. to make our appointment, and it looked like we’d be driving right with the advancing storm as we backtracked to Boerne.

By 5, we got some rain, but no hail. We started driving and it was dark and rainy and windy, but nothing too frightening. We were at the Mercedes gate as it was unlocked, and Daniel got us right in. They determined the two “downstream” sensors needed to be replaced, and by about noon, we were back on the road, under clearing skies.

We headed for Junction, Texas, to regroup, took a nap, then a walk around town, where we found the roof blown off one of the churches, roofing from the local diner wrapped around a street sign and insulation and broken glass along the sidewalks. A local law enforcement official told us they were still waiting for the National Weather Service to classify it, but he believed a small tornado had touched down overnight. Luckily, no one was hurt.

We rolled to Junction’s city park, a lovely free camp spot along the South Llano River, where we sat by the water, feeling wrung out but resilient, watching a fisherman throw out his line from a small skiff and a hawk circle overhead, his wings catching the glow of the setting sun, believing that tomorrow, we’d head down the road toward Arizona, unimpeded by weather or dash alerts.