Heads up for tow vechicles

I have a 2006 F-350 Dually long bed and a brought it to the shop today due to a charging issue. I had the mechanic check out the truck to be sure there were no other issues. Upon inspection, he noticed that the 3 beams that hold the trucks bed to the truck frame were rotting. I notice the rear one and it looked like swiss cheese. With this situation if the "beams" failed I could loose the bed or if towing my 5er. I have very light miles on the truck for its age, so that has nothing to do with mileage, but age and salt. The truck was purchased new in New England. A word of warning, is anyone that tows should also occasionally check their vehicles frame integrity. I was told that I could either find a "junk" bed or a welder who would remove the bed and replace the supports. est. cost $1500 to $2000 per phone conversation.