If that is all your looking at I would replace the panels, I had to find and buy the lunette, casting and make new "A" frames that alone was $375...
I have had to make almost all the brake parts; save the brake handle it was bent up pretty bad, I was able to straighten it out... Need to replace the wiring and brake cable along with new tires...
In my opinion if you can save your trailer for $400 go for it, it will be worth the expense sometime down the road... you got to remember an ORIGINAL M-100 is a limited quantity...
My tub is not perfect... it has dings and dents I could not get out due to time constraints (NO room in the garage and the rains came last night

). However I have cleaned all the rust and old paint off, reprimered and repainted all the parts. Rebuilt the axle and lubed all the parts. I got the axle and shocks mounted yesterday, I ended up using the rubbers that came with the shocks, the new shocks did not have tapered mounts to fit the new rubbers I bought...
I will not have a show winner, but it will be correct and original to a point, and mine...
Besides, with me putting money into a restoral I have something to show for it as opposed to the folks that drink their money and have nothing to show; except for a retirement belly...
Hope this helps...