I've had the unfortunate pleasure of working on this exact problem a couple of times in a Motorhome. I can't speak to the design in a tent trailer but the fix I did last time was a winner. I did not pull all the furnishings out to accomplish the task although I was able to expose at least two metal cross members in which to start the mending process.
Pull out as much rotten wood as possible, in a tent camper removing large items and cabinets may be an easier task? Make a long story short, I used steel uni strut along with dimensional lumber as my new outriggers thus eliminating all sag. Laid down exterior plywood(3/4" in my case) and since I was going to tile some area's, I put Hardy board down in other area's I used wood flooring. Six years later and all is still SOLID with no cracked time.
96 Vogue Prima Vista
The Kid's: Humphrie, the Mini Schnauzer and Georgie,wire haired dachshund.
Rainbow Bridge: Laddie,Scoutie,Katie,Cooper,Kodie,Rubie,Maggie, Cassie, Mollie, Elvis, Potter and Rosie Love You! (40+ years in all)