I've thought about getting one a couple of years back but there hell-ishly expensive to buy even on the 2nd hand market!
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I did think about getting something like a Transit size van or minibus and then converting it with a bit of help.
Did a bit of homework and would of been cheaper than buying something that's already done.
I may still do the idea in a few years time when my riding days are over, mind you when it gets to that time I may also have to think of fitting a chemical toilet as well, as I won't make it to the camp site ones in time!