PortaPotti height

Hi All,
I'm just in the final stages of my conversion of an 07 Citroen Relay, it has already been used for a very successful week away and all that is left is the cleaning up, painting units etc. One problem that did surface on the test run, was that the Porta Potti is very low; it could be described as a knee-cracker! Our old Pilote had a cassette unit which gave a good seat height so this problem came out of the blue.

When I was researching which Potti to buy, I remember seeing an advert for a plinth, specially made to raise the height by about three inches. Now that I want to buy one, I can't find it. Anyone any ideas on where such a thing can be bought.

I've done all the carpentry for the bathroom, beds, kitchen units etc, so making one wouldn't be a problem - except that I would rather it be made out of plastic for hygiene reasons.

Ian