As it turned out, the tubing was snapped off, not the weld. I totally removed the platform and loosened the paneling enough to get to the broken rail. I then used clamps and 2X4s to torque the bend out of the rail that occurred during the breaking process. I then sandwiched nearly the entire rail in two pieces of 1/8" angle aluminum and used 5 worm gear hose clamps to hold them tight to the rail. Next I put the paneling and plastic trim back. You can't see the repair unless you remove the mattress.
In analyzing what went wrong, I discovered many screw and staple holes created during the original build. The break occurred where a number of holes were drilled close together and the rail strength was compromised. In my opinion, the material Forest River used (1/16" aluminum tubing) was way too thin for the job. I elected to reattach the panels with automotive double-sided tape and a minimum number of screws.
I only fixed the broken rail. The other was straight and looked OK.

I do have photos of my repair, but can't find a way to post them in this message, ... I used mending plates from Lowes, attached them with screws on both top and bottom of every joint, ...on the broken weld joint, I also added 90 degree pieces on each side of that joint, ... honestly I believe the repair to be a better fix than the welded original condition, ... to do what I did, did require a complete removing of the frame, but you may be able to fix your problem without that much work, ... after removing some of the base wooded panels, you may see that your brake can be repaired in some different way, ...

I noted that you tore the Murphy Bed apart to make repairs. Is it as grueling a job as I imagine? How well did it go back together? Do you have pictures? I have a broken tube (not just a weld) to fix.