Not huge fan of porta potties. In preparation for our build, I have accumulated:
a 20L bucket,
an oval shaped funnel,
a paint mixing implement,
5L plastic petrol can
and a basic toilet seat/lid.
The funnel fits perfectly the curve of the inside of the bucket, so theres the separation of liquids/solids taken care of.
Left to buy is some pvc piping and computer fans for the ventilation.
Not sure about the source of peat moss here in Aus. The stuff from Bunnings has potting mix bacteria in it, which the wife says is not the right stuff.