The more bends you use, the more clogs you'll get, depend on it. And every second bend or so should be a cleanout to deal with those clogs. Do you LIKE working with old poop?
RV black tanks are directly below the RV toilets so they drop stuff right in. They do NOT use bends.
Domestic toilets are right by the main drains, and use all of that water to flush stuff down the pipes. Unless you plan on HUGE fresh and black tanks, don't use a domestic toilet.
Besides, RV toilets start at $90 or so for portable units, similar price for fixed units. Go with an RV toilet, and keep the thing right over the tank.