One of my easier mobile base designs went like this:
(Picture to be added when I extract its wreckage from the gut of a fungal bloom)
It was an RV that I’d expanded by three tiles vertically and one tile horizontally (I just seem to spend a lot less time running into walls I didn’t want damaged with cars that are longer than they are wide). And pretty much what everyone recommends for a mobile base-namely cooking, welding, and food preservation implements, and stronger frames and plating. The only weird thing I managed to add was a “wine cork” bumper made of spiked and hard plating.
I thought it might help in securing big buildings with very few entrances-by ramming (and of course destroying) the door/s and getting out of a door in front while the hard shell of the reinforced RV kept critters from flooding the place. Then I’d storm, loot, and retreat. The Cork had a V8 engine and one V6 both under the seats, so it could back into a horde and get out barely dented running.