It really isn't hard to do if you know what you're doing. Hopefully the posts I made in this thread will help.
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Barn-door To Tailgate Conversion
The key to my conversion was buying a rear lid, bumper, lights and in fill panels all in the right colour. It certainly transforms a van into something much nicer to tour round in.
The mechanical swap is easy but many are put off with the wiring and coding. Its actually quite simple but just takes time/effort. If you're paying someone to do it all and wire in the wiper, heated screen and add the screen wash pump, it really won't be cheap or worth it. It's a DIY job.