How should I cover this whole in my bed?

So I was cleaning my truck when I noticed inside my bed the front driver side camper bolt that goes thru the rail was missing it’s nut, on closer inspection I noticed a whole in my actual bed, it appears when they installed the camper they were drilling a hole through the rail and accidentally drill into the bed. There was some minor rust around the hole so I sanded it all down to bare metal and painted it, I’m planning to spray some fluid film thru the hole to mitigate rust

any suggestions how to cover the hole? It’s pretty small and the area isn’t flush and it’s right underneath the rail so i imagine welding would be a major pita nightmare, best solution I could come up with so far is put a piece of rubber and then duct tape over so no dirt or water can get in

 

Maybe a black RTV will work.

 

https://flexsealproducts.com/products/flex-shot?variant=32929718403181

 

Can of bed linner, maybe several coats will fill the hole in.

 

JB weld and then bedliner

 

I used JB weld on a rust hole on the side of lawn mower and it worked like a champ. Just put some duct tape to cover the outside of the hole, then fill the hole with JB - then pull the tape off after it's dry.

 

Drop the JB and do real