There was a post about doing this over on the General Forum (I believe). Anyway, guy removed toilet x 40 years of RVing and put a porta potty in its place for winter camping. We only have a 5 gallon Thetford curve porta potty in our TC. Love it. Use septic safe chemicals and dump at home right into the regular toilet. We dump every other day b/c 5 gallons is a decent amount of weight to handle...
If you have enough room to put it in the shower. Do it. If space is an issue remove the toilet, and make a small riser (will bring porta potty up to comfortable height) to go over hole. That'll solve all problems.
Kinda gross, but one good thing with a porta potty is the ability to carry it in the back seat of the truck if you need to thaw it out! Just don't get into a accident! LOL