No, tanks and batteries cannot share tiles. Any tank up to 60L is installed inside the frame itself. The 200L tank must be mounted externally.
As for what you want in a deathmobile, I’d personally recommend military composite armor plating and heavy armament. Go nuclear electric if you can. Minireactors and solar panels, with lots of storage batteries.
And wherever you sleep inside it better not be visible from the outside, or you might wake up with something trying to eat your face. Curtains can be mounted on quarter panels to help with this. I personally use a reclining seat surrounded by stowboards and opaque hatches. No curtains needed, and it doubles as a secure cockpit for my tank.
I also highly recommend Shard’s Misc. Mod, it has some EXTREMELY useful vehicle parts if you can scavenge enough to make them, and some useful game tweeks. They really simplify storage for power and loot.
This is my personal vehicle for reference. Made it out of a tank I pillaged from a national guard base. Pulled the 30mm cannon and ATGM missile launchers off of a couple infantry fighting vehicles or something. The storage tanks are very useful for cutting down on space in your storage, so you don’t have a hundred gallon jugs of bleach laying around.
Note: You probably don’t NEED this many weapons, but I personally don’t believe in overkill.
The automated Lascannons are definitely not overkill though, and are extremely useful for killing hordes or swarms coming at you, or securing an area while you loot.