Used to use one in my MH when I left from up North in the middle of winter with a fully winterized RV. I hate public restrooms so I would set the porta pottie next to my toilet in the bathroom in the MH and use it until I hit warmer weather to de-winterize the MH on the way down to Florida to use my water.
Thetford makes GREAT porta=potties there are
exactly the same 'fit', so to say. as all standard toilets in RV's. All different models to choose from and all different size holding cassette.
They have a removable cassette that attaches to the bottom. I have NEVER smelled anything from it. Easy to dump in a public toilet or dump station. Actually I found it less offensive and less smell than dumping my tanks in the MH !
They come in all sizes and one even comes with a battery operated flush in case one is too lazy to push a button manually!!!!
Walmart carries one for 65.00. Be careful though sometimes they substitute an off brand for the Thetford one.
Here is all you ever wanted and/or needed to know about porta-potties and models to choose from:http://www.thetford.com/HOME/ApplicationHome/RecreationalApplication/tabid/85/Default.aspx
Don't forget the

!
:B