I just removed my tool box permanetly off my truck, and am wondering the best way to fill in those holes that were drilled through my plastic cover on the edge of my bed as I dont want water to start getting in there and start rusting out. Any suggestions please.

 

I'd prolly use a sealer /rust preventer something maybe like Rust Bullet or the like.

Personally I wouldn't be able to live with the holes so I'd most likely replace the covers.

But in this case perhaps filling with silicone or simply putting a rubber body plug in the hole may work as well.

 

mix up some jb weld and use it like wood puddy in a nail hole.