I 'd say bondo and sand that beyotch...then maybe find or buy some corner protecters to help that corner...The back of my Mr Do cab has the top layer of the plywood peeling off...I went and tore off what was hanging and filled the gaps with wood filler and sanded it smooth...
With the bottom being in that condition, I would use bondo or wood filler and lay it thick and sand smooth... if you can get away with it...maybe also drill some flat screws to hold that wood to the cab...then bondo over it...also when you paint it..the paint will hide the inperfections...
Another thing also...is that only you will know where the inperfections are...unless you have anal friends who come over and say "Hey that bottom looks rough!"
** just saw the post from Ed**
If it major ...i would follow the thread...
Now I do not know if this goes all the way through, I dont think it does,
Now from the photos, it looks cosmetic...you might can get away with just the bondo/wood filler
You probley dont want to do this....( the cab is like your child)..but take a screwdriver and lightly stab where you think its rotten...if the wood is bad...use that thread....