i wish i could come up with a product and convince people when it screws someting up it just works too good, but as i mentioned that would be a thread for the detailing section, as far as using a truck bed coating on the plastics goes, there are a lot of good options, the upol raptor stuff is really good i rolled it on my cousins truck bed (6 years ago) no cover on the bed and the stuff looks almost new to this day and iirc you can get a kit with a spray gun for the liner if you have a compressor that will supply enough air to run it. more importantly you need to look into what prep is required, the unpainted plastic will always be a bit more involved than painted parts, you'll need to scuff and wipe down with alcohol at a bare minimum, look into the products and find out if an adhesion promoting product is needed etc...