2000 Monaco Lapalma 36G bathroom remodel toilet riser box questions

[Q5Grafx]

so i have a 2000 monaco and the toilet riser box is carpeted. i have redone the rest of the bathroom already and have purchased a dometic 421 lo rise platinum toilet to replace the sealand traveler that it came with. the wood under that carpet is disgusting and i dont want to put my new toilet on it. i am reflooring with a pvc plank flooring solution. problem is the 10000 staples holding the carpet on but once i got under the carpet found out the wood isnt rotten but thoroughly nasty and dont want to waste all the time pulling out 10000 staples from pissy stinky wood. I have new 3/4" marine grade plywood to rebuild the box but cannot figure out how the old box is attached. everything else like the hose covers had screws bolting them to the floor chipboard. they carpetted all sides of the box before installing it and there are no screws holding the box to the floor. what im wondering is if anyone knows if the box is held down by the flange mount screws into a structure under the box. I am living in this RV fulltime and cannot go a very long time without the toilet working as im old as dirt and have to use it alot. also the new toilet is about 2" taller than the traveller that is currently in it and was wondering if i could lower the height of the box. I have the entire front of the box's carpet removed and one half of the top but still havent found anything that would mount it, not a single screw anywhere.