To fix the frame flex, there are not many options. We had ours fixed by Truck Builders in Marion, IA. We were able to stay in the rig for three days while they made the repairs.
The welders you talked to gave you good information. Some of the aluminum has to be welded also. For our unit, Truck Builders not only welded gussets to the frame next to the king pin, but they also inserted three large bolts on each side of the rig from the propane bottle area (we have a propane bottle on each side) through the wall to strengthen the front end to the rest of the RV chassis.
If you'd like some information, you can call Truck Builders at 319-377-5670 or e-mail them at
TruckB@msn.com
Ask to speak to Tim Wentz. He's the owner and will give you some good advice. Tell him that Orv Schinke recommended that you call him. He'll remember what he did to our rig.
Orv