A friend of mine who does maintenance on remote radio towers built something that sounds similar.
He started with an F550 4X4 cab and chassis and had a company that builds 'expiditer' trucks (the bunk is inside the van body) build him what is basically a 16' sleeper cab / box with an over-cab bed.
There is no connection between the cab and the box, but other than that it's basically a C m/h but with lots of CCC and huge trailer towing capacity. He tows an enclosed cargo trailer with all his gear including a genset.
I don't know what it ended up costing him, but he said it was about half of what a 2WD Super C would have cost. It is a little less 'frilly' and refined than an 'RV' would be, but it was all there and quite functional. He's been living in it and working out of it 8 months a year for a few years now it seems to be holding up just fine.