Welcome to the TC Forum. Lots of experienced and helpful people here. Just be prepared that not everyone will tell you what you want to hear, but share their best advice.
There are some TC Manufacturers that build full width (flat bed) type TCs. Four Wheel Campers and Northstar come to mind. Check the history in Truck Camper Magazine, as there are a few articles on this subject, as well as information on Fulltiming. Just be prepared a project like this takes time, up to a year to put together, so if your plans are to start right away, like this fall, you are underestimating the work ahead.
Good luck.
b