i have a couple spots in my bed on top of the wheel wells.









my question is, should i try to cut the rust out and weld the patch INTO the bed, or simply weld the patch ON TOP (with or without removing rust)? i bought some 1/8" thick steel tread plate planing on welding on top but am having second thoughts about that. if i dont use the tread plate there, i'm sure i'll find another use for it

either way, i'm gonna spray something underneath (either undercoating or bed liner) to prevent further/future rust.

 

I would want to cut as much out as needed for the patch to sit on good metal. You wouldn´t want to lay the patch over thin, partially rusted material. That could cause future issues. You don´t have to go crazy with the cutting out, just get the thin parts out and take a grinder to the surface rust on the thicker portion. Doing that along with you going to do an undercoating should last a good while. If you cut out most of it you could probably come from underneath and tack on some support material, cut the patch to fit and tack to supports, then a nice bead along the whole thing from inside the bed, grind down, and do the bed with herculiner or equivalent spray on/roll on bed liner and it would look good.
Good luck with the repairs.