In our old camper we had 60 gal fresh, 30 black, 39 gray. We could go 5-6 days in 90+ temps at a music festival (using their facilities while inside at the shows) and never come close to running out of water or filling up the gray, black would get close but not full. That included a daily navy shower for me, one around every other day for my husband. Very little dishwashing, usually just a quick rinse for stuff like knives/cooking utensils and using paper/plastic for everything else.
We have always had an onboard generator so I can't speak to that side of it, other than saying we did have to fill up the onboard fuel tank for the generator a few times since the AC was on a lot.