Those things are possible. Most here use Hondas or some other portable generator. I do have an Onan in my van. Very noisy though. I also have a Honda.
If you have a short wheel base, the inside shower is of course more of a challenge. Maybe one like some of the Roadtrek’s have with a shower pan with removal cover/pan in the center of the floor.
2008 GMC 3500 Quigley Weldtec 4x4 Savana SMB
2006 BMW HP2 Enduro-Sold