I have some rust on my wheel well. I want to do the roll on Bedliner on the wheel well and trim. What do I need to do to get rid of the rust.

 

There's a little more to it than bedlining it and calling it done if you want it to last.

Rust is like cancer once it starts you have to removal it all to get it to stop.
-Protect the paint you don't want to mess up with tape and newspaper
-remove the rust (grinder, palm sander or wire wheel) I prefer wire wheel on a mini grinder then light grit flap wheel on mini grinder.
-wipe it down and prime it immediately, bare metal will begin to oxidise quickly.
-apply your bedliner when primer is dry. Self etching primer is nice too.

You could go as far as body filling as well but if you're going to bedline it's a thick enough product that you wont notice imperfections anyway.

That's my 2cents, I've done a lot of that in my driveway, it's never looked perfect but it works.

FYI Don't do what I'm doing and just keep buying bigger wheel flares lol

 

I would do what Bad told you but, prior to primer, I would hit it with some rust inhibitor .. it will prevent the cancer from spreading any further. Loctite makes some great stuff in a rattle can ...got mine at the Home Depot.