You're first task is to determine exactly where the water is coming from. I had a leak on our old hybrid that appeared to be coming from the front bed. It was actually coming from the roof seam where the crowned piece of aluminum joins the roof. I caught it early and it was easily fixed by opening that part of the roof up, drying it out and sealing it with Eternabond tape.
For the floor it's no different than any other trailer. We did my dad's old '77 Jayco probably 10 years ago. Construction on these is actually very simple.You may need to remove the front cabinets if it has any. Once you are in the floor, since the floor is one piece that the walls and cabinets get attached to, you might find that the wood is rotted beyond and under the wall. All you can do is dig it out and work a replacement board into the slot you created.
If you have to rebuild the front wall, then the above really doesn't apply, but that's not all that hard either. Take your time taking everything apart and see how it's constructed. You'll end up putting it back to together with better quality workmanship than when it was new.
Chuck D.
โAdventure is just bad planning.โ - Roald Amundsen
2013 Jayco X20E Hybrid
2016 Chevy Silverado Crew Cab Z71 LTZ2
2008 GMC Sierra SLE1 Crew Cab Z71 (traded)