I had to make a repair to our TT early this spring for a soft spot/leak. Your plan sound reasonable. I had to cut ours to have the access I needed. I replaced plywood and used eternabond on the areas I had to cut. So far, so good. I would have some on hand prior to starting, IMO.
2009 Outback 268rl
2015 F250 Lariat 6.7 Powerstroke