I removed my water heater (Suburban 6 gallon propane) because it was a bit munged up. I bought a new one but then realized I really don't know if I need it, and I DO know I could use the extra space!
As far as removing, I just disconnected everything and plugged the propane line (was a 3/8" female flare) with a 3/8" male flare plug. For now just on the very end of the line in case water heater "wants" to go back in. I'm not 100% sure about not having one, but since it's out now (new one in box is at the ready) I'm going to try it without for awhile.
Here is what I'm thinking on the door/opening:
1) I will use it for outside storage for things that wouldn't be "killed" if they got wet and are not valuable. Hence I can use a regular water heater door there. I'm thinking Lynx blocks and maybe water hose, etc.
2) The way mine (Suburban) is designed the water heater door flange makes a seal with the water heater itself and that is what keeps (kept) the elements out of the van. So I'm thinking to fab a lightweight box of some sort that is around the size/shape of the water heater, and that will be the storage box that is accessible from outside and interlocks with the Suburban door/flange. That way if water gets into the "box" it stays out of the van, just like the original. I'll still probably cover the back of the "grates" in the water heater door/flange unit and also slope the bottom of the box to drain outside. Still in planning stage though and all ears if anyone has thoughts/ideas/etc.
3) This is easily reversible to put the water heater back.
For sink/dishes/hands, I'm 100% fine with not having a water heater. I'm not used to it and have been heating water up in a kettle when necessary for ages (on boats). Even with the water heater it's far enough from the sink that there is either water wastage waiting for it to "show up," or I have to first collect the non-heated water in a container and save it (a pain).
For the shower.... well, there is where heated water would be nice. I have yet to come up with a way to heat water in a kettle and "stuff it" into a place where it would come out the built in showerhead! I have used a garden sprayer on boats, but that is then something to store (and ahem, around the size of a water heater...). OTOH, it can easily be toted outside, which is a plus. So that's the one thing that's been slightly holding me back, but as long as things are easily reversible (i.e. I can easily install the new water heater I have sitting in a box) I think I'm going to give it a try.
Ultimately if it worked out, I'd think about laying up a fiberglass door instead of the slightly-awkward-to-use water heater door, but that's way down the road, and the water heater door (outside door to storage compartment) may work fine.