If you're handy in the plumbing department go for the hot water heater, fresh and grey water tanks. There are units available that are potty/shower combos which make a wet bath with a built in black water tank and shower drain either fires to the holding tank or "blue boy" but size available in you're camper can be the issue. In lieu of inside shower maybe install an outside shower with a long enough hose to extend to an outside shower tent and use the pan ideas. Our old camper is only missing a grey water tank and we drag along a blue tote for that when there are no sewer hookups, which is often in small or out of the way places. I worked on our old camper since getting it last June, as we could afford it and the camper stayed usable, if not fully functional, the whole time. Just did my last item on the list yesterday with the addition of a rear door awning. Had one I'd made but this ARB BAG awning is more substantial and was the only one I could find to fit our awkward and limited back end. The ladder is too close to the door for anything with support arms fastened to the wall and couldn't justify over $1,000 for the auto ones that fold toward the center from each side, our ideal. Anyway, probably a case of TMI but I have much more pride of ownership in doing all this work mostly on my own with professional assistance when I felt out of my depth. Good luck, on modifying and Happy Camping.