has anyone ever done this .......

[scottie]

cut the rear of off a van to make a motorhome ?

not just convert a van but cut the rear of and made a living/sleeping unit like a purpose made motorhome ?

[dumper]

It has been done I think some conversion company used to do it back in the days of the mk2

[Chug]

I think you would have all sorts of problems with dvla, it will probably need an engineers report for a minimum, you would probably be better off with a chassis cab.