I had one in my van when I purchased it.  The box was pretty simple.  had three sides and no front for ease of puling the toilet out for cleaning and accessign hte pull lever to dump your dump.  It had a flip top lid that opneed so you could squat or sit.  It made a great step for teh top bunk.  I wish I would not have gotten rid of it.  
 
 

 
> Date: Wed, 28 Jul 2010 13:11:56 -0700
> From: becida@COMCAST.NET
> Subject: Porta-potti boxes
> To: vanagon@GERRY.VANAGON.COM
> 
> For the traveling we have been doing this summer I bought a
> porta-potti for the bus. Well, I actually pulled out the porta-potti
> I already had and one of the side clamps had broken off the body so I
> needed a new one. The old one is one of those square jobs with
> plastic accordion type water pump, clamps on the side to keep the top
> & bottom together and the pull-push dumper valve (I saw them at
> K-Mart and Sportsman Warehouse). The new one is a longer version from
> Coleman with a hand pump for the water, the top/bottom attach by
> twisting the top onto the bottom and the dumping lever goes side to side.
> Anyway I have the toilet sitting in the Westy just behind the
> passenger seat, it does the job but really looks like a toilet. I
> need to put a box around it and that box requires a bit of
> engineering as you have to be able to have free access to the whole
> top for use and the lower front for opening the dump lever. As a plus
> the toilet needs to be removed from that box everyday that it is used.
> 
> I'm thinking at someone (or two) on the Vanagon list has already done
> this engineering and can point me in the correct direction or maybe
> even point out some problems with this project.
> 
> Anyone with experience in building a toilet box for the Vanagon?
> 
> 
> 
> Rob
> becida@comcast.net