Working as an RV Tech the last little while, I have had to repair several. I have found the best method is sheet metal, like you said, screwing it to the floor, (look in the camper for electric and water lines), and then covering with auto undercoating, the rubberized stuff. This seems to work well.
As for your complaint, about that area being stronger, no manufacturer plans for a blow out. Remember a few years ago when a bus blew a tire and the tire came through the floor and hurt several, might even have killed one, (memory)?
2012 Ford F250 ext. Cab 4x4
2002 Jeep Wrangler Sahara
2008 Yamaha V-Star 650 Classic
2008 Work and Play 18LT