Easy...........
My first job was a coach trimmer and fitting vans out was part of the work.
a) The equivalent price of a decent T4 camper van starts at £9K+
Mines a 1 owner FSH minter - did'nt cost me anywhere near £9K
c) I can build it to my requirments for example furniture will be fitted with wingnuts for easy removal when needed as a van again.
d) I dont like some of the commercial conversions they use chipboard furniture which weighs a tonne!
e) You can buy all the fittings off the shelf - fridges, sinks, ZIG units, pop tops, side awnings etc
Basically cheap camping