Never really got into deathmobiles, so I ended up gravitating to making bases. In any case, usually I just repurpose rooms to become big storage areas instead of making multi-room bases. Mansions, sewage treatment plants, the locked middle room in refugee centers, and the odd house here and there. Firestations can also be nice, though that one can be real vulnerable to hordes depending on the location.
That said, when it comes to vehicles I still make them fairly large. 4x5 cargo carriers, armored everywhere, and can generally plow through several tiles of forests before needing repairs here and there.