I have decided to stick with a luan + foam + luan sandwich. I have found both with the foam being in the correct density.
After ripping into things it isn't as bad as I thought it would be.
There are two frame pieces about two feet into the rv that run length wise and then cross frames every 30 inches or so.
I will replace a section 30" by about 6 feet and another section 60" by two feet that encompasses the front door.
I will add some cross members between the side-to-side frame pieces made from angle iron bolted into the existing frame pieces for the new floor to sit on. The new pieces will be glued to the existing floor creating a solid connection.
Then I will cover the entire floor (after removing the existing vinyl) with a top grade sealant/water proof coating like what is used in a shower.
On top of that I will add vinyl planks glued to the floor.
Upon further inspection of the rv, I noticed that the awning doesn't cover the back end of the slide offering a great place for water to get on top of the slide or into the seals. I am going to see If I can slide the existing awning cover towards the rear so that this area is protected. There is at least 10" of empty space. I think the awning material could have been a foot longer though and I wouldn't have this problem.
Appreciate the help.