Hi Rod,
What I have done is along the lines you are talking about.
We bought a camper trailer top.. $1800. from a dealer online,, comes as the tent and a hard base, ready to mount on a trailer.
I raised the sides of my 6x4 with some box section steel, just welded on sides tail gate etc.
Put 4 mounting brackets on the camper.. corresponding bolt holes in trailer,,
built a frame in the shed,,
now just slide the camper on or off as required,, still got my trusty 6x4 for all thos things we do.
The company we got our camper from is
"trailercampers.com" NOTE,, this is an online company,, and you can google them.
they are a Tassie company and make a good setup.
We collected ours from Sydney where they have a depo.
if you got any Q's just ask,, have had a few pitfalls but got most worked out now.
Cheers Stan