The important thing I would say is to arrest the rust so after wire brushing and using a sanding block (I prefer my 5" orbital sander where it will reach) spray a rust converter first and then top it with the bedliner spray. Or you can go the more expensive one-step route and use POR-15 (if you don't mind the texture you don't even have to sand/wire brush first unless the rust is flaking of course plus you can roll it on and it dries smooth). I know they recommend top-coating the POR-15 since it doesn't have any UV inhibitors but I would use it anyway and just top it with the bedliner spray in the wheel areas. This is a project my lazy butt has been wanting to do for some time.
BTW, I think that bedliner spray will stick to just about ANYTHING! Definitely a Jeeper's best friend.