What are your mobile bases like?

So I want to build a mobile base but have no idea where to start. Should I find an RV and put tons of solar panels on it?

depends on what you need
need water? tanks and a kitchen buddy
mobile? electric motors and solar
fuel and power? get a hose to feed the beast stick to gas
most everything? get a forge up you’ll need some hard plating

I mostly just want water, food(if possible) and crafting. Can you activate a funnel to an attached tank on your vehicle?

no but with a proper funnel you can install it over a tank

Also, what spot needs to be open to install a tank? Can there be a battery and tank in the same spot?

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.

I second the lasercannons, or any energy weapon for that matter.
I normally start finding an APC or similar, and then installing a welding rig and solar panels on it, they’ll power up your other modifications. Then you proceed for the other crafting rigs, cargo space and whatnot. Floor trunks are awesome too.
This goes a bit against the common recommendations around here, but try to not make you Deathmobile too heavy for its engines. Long-distance travelling at 90km/h gets boring FAST. A V12 engine can easily drag 11T+ of weight (probably too OP), so once you find one your mostly set.