Have you used a toilet shower combo? Pretty cramped quarters.
A really easy alternative is to use an aisle shower. I'll admit that my DIY is quite rudimentary--I use a $4 HD mortar tub to capture the water and two shower curtains hung from the ceiling. Not difficult to empty a couple of gallons of water afterwards.
(The truth is we have a fabulous warm-weather shower---a shower "sock" envelopes the open back doors and we get a 28"x56"x96" shower stall with the mortar tub at ground level. Elbow room and a scene from Petticoat Junction)
Sorry to not answer your question more directly....good luck with your solution!