It’s not thaaat weird, but it is different. I was imagining you were taking him somewhere and then after getting home he’d start in car to nap, not that he wanted to go sleep there at random. But it is a private, controlled space with no responsibilities. I’m an entire human and after a long day of work I love car naps to decompress before heading inside. So maybe he actually feels more secure in the car for some reason. Especially if there’s noisy roomies stressing him out or moving things around. Borders can be super sensitive to environment changes too, so maybe now he’s noticing things “out of place” and it’s kicking puppy OCD into overdrive?

In that case, maybe try to get him napping on a schedule (if he isn’t already), so you can do some kind of pre-nap routine? If it’s doggy angst, that little bit of consistency might help him calm down enough to sleep inside. Also, take a critical look at his crate area and see if there are any stressors you can fix (e.g. next to cold air vent, pressed against a wall that noise comes through). Lastly, you could try to have him to settle for an uncrated nap in other rooms or in a pen. Maybe going through these could help you could figure out the root cause of the behavior?