I did not have the issue but did the repair as a precaution. Here’s some pics on my 2023 310rl. Not to hard of a process. I would recommend using the exploding rivets not the tri fold rivets. I used old oak board saw to correct size and pre drilled the holes. Back wall angle iron on floor was still tight so I just drill holes and added the rivets. I would think if it was done at the factory you should be able to remove the plastic that covers the screws on the rear wall and see the bigger screw like in 4th pic down (if the factory fix is the same on the assembly line).
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Nice work and documentation. I actually varied from the Alliance plan...I had to go back to what Alliance sent me and yours was done correct to their documentation. I choose to place their corner metal at a different location (I bought a thicker corner bracket as well)...I placed mine to connect frame tubing to frame tubing. I also added the lower bracket, they did not have as additional strength. I was having a hard time, understanding why the bracket they sent, buried a screw in a short piece of wood. Mine looked like yours, where the wood did not extend to the end of the tubing. Those needing to do this repair, might want to consider the two different approaches. UFF, did it exactly like Alliance says....I did it differently...after all, it was Alliance engineers that made the first design...LOL!! Glad you finally got to the fenders!!
