I am building something similar.
The reason for me is that I have a spot on my lot where I would like to build guest quarters. I went to the county and was told that I cannot build a permanent structure there. I can, however, erect a "temporary" structure or park a trailer. Their definition of temporary included the RV shelters that are common here as long as I don't pour a slab or foundation. Trailer would include a 10' wide "jobsite" trailer.
I purchased an 80's model 5th wheel and stripped to the frame. This spring I will build a 10' x 30' structure on the frame. It will be of standard 2x construction using standard materials and be well insulated. It will still be a highway legal trailer (oversize permit required) but will probably not ever be moved.