[Wavery]

I think that I might be tempted to remove the stove and the cabinet door under the stove. Open a 3" high by 6" long hole just above the floor. Fold the aluminum skin down, flat on the floor to expose the area just above those bolts. Scrape out the styrofoam. Take out the center bolt and drill a hole straight through the floor and into your new opening. If it looks doable, get a 4" wide x 6" long (or longer) 10G or 1/4" steel plate and drill matching holes for new 316 S/S bolts (5/16" X approx 5 or 6" long) to go all the way through the trailer frame and about 1.5" into your opening. Put S/S washers, lock washers and S/S nuts with some Blue Locktite on the bolts and tighten it to about 15ft pounds (as to not crush the rotten wood.

These are not instructions......... just brain storming. Wait for others to chime in. I've never opened the wall there but I would certainly try that before I'd try to replace that 2x4 wood floor frame.

Just another though....... if you use 1/4" steel plate, you could just tap the holes with a 5/16-20 standard tap. Just be aware that might make it harder to get the new bolts started threading.