Sorry about that. I wasn't more spacific.
I meant on the underside of my truck bed.
I already have most of the inside of my tuck bed prepped for liner.
Just wanted to know if it would be a good idea to protect the uderside
before I sprayed the inside.

 

That is my intent. To take bed off and undercoat bottom of the bed and wheel wells with the Rust-oleum and do the frame at the same time and then do the bed itself.