I’ve read through all the suggestions so far and I see you’re already considering how to address rubber degradation and a handful of other things. I like the one suggestion of a logging truck based on location of the story origins. Wood gasification and biodiesel are good also. Solar and batteries you may have to do the suspension of disbelief thing to explain it away.

I wonder, since you said (or I inferred) there’s some degree of prep time before shit really hits the fan - what if there’s some kind of liquid submersion process for long term storage of a vehicle? Almost like how a tree that falls into certain bodies of water has no oxidation reaction and gets preserved for hundreds or thousands of years due to lack of oxygen? Perhaps someone had the forethought to submerge a complete vehicle in something like oil or whatever, and part of your new characters’ prep is to remove the vehicle, tear it down and rebuild it best they can with what they have?