RE: Porta Potties
One of the first things I bought nearly 20 years ago when I bought my first
Westy was one of the flushing chemical toilets (replaced after ten plus
years of use with the identical model) and still use on a regular basis.
 As for containment mine did not spill or leak when I rolled and totaled my
'85, no damage either.  It went right into the '90 Westy that replaced the
'85 and continued in use until a crack developed in the flushing water tank
and it was then replaced.  Absolutely indispensable.