Minimalistic toilet setup in a traveler's trailer
Here in the UK, we always use chemical toilets for this sort of thing. They have a removable waste tank built in that in many models can hold at least a person-week's waste, and the chemical keeps it from smelling for that long even in hot weather. The capacity lasts a lot longer if you don't use it for everything. Emptying can be done into a normal toilet (e.g. at home) or at an emptying point for RVs, and the chemical additive is available in a type suitable for septic tanks. Most use a cassette tank that's removed through a hatch on the outside of the vehicle. 

I'm sure you can buy the chemical in the US, whether the toilet is available is another matter. Brands over here include Thetford and Porta-Potti. They're usually made of plastic so are much lighter than a domestic toilet, and also use much less water to flush.