In your case, I would very seriously consider:
a) Moving out of town - with no mushrooms - and find new vehicles to butcher - in another town (or another galaxy, if mushrooms spread too far)
b) making portable/foldable crane (fabricate folding frame; fabricate Telescopic Cantilever; get ahold of casters from shopping cart; create new vehicle with folding frame you made; put Telescopic Cantilever on that ‘vehicle’, put casters on = now you have portable folding crane)
c) Now you can unfold your portable crane and drag it around just like shopping cart (Shift+G) to take off or install parts. (E)xamine that crane to fold it and put in your backpack or carry it when you’re done with repairs.
d) if wall is in the way in your own vehicle - take wall off and install a door instead. Zombies can’t get in… except for Mi-Gos and Ferals… but you can open the door to get clear line of site.