This is a very simple solution based in a 5 gallons bucket toilet (basically a seat of a common toilet installed over a plastic bucket). One good thing about this model is that you can use a trash bags (13 gallons size works well). To facilitate disposal some people put cat litter on the bottom.
We can say that the points of attraction here are:
- Low price
The only negative opinions I’ve seen come from tall people and they are in reference to its height.
Last, coming also from Reliance, there is the Fold-To-Go Collapsible Portable Toilet which is so compact that can be fold to just five inches.
Disclaimer: I based the selection in checking buyers popularity and reading multiple reviews; for the camper I own a Visa Potty (check available models here), but the design even if good may be a little bulky for some applications. Note that there are affiliate links in this page.