what is a good way to prevent rusting around the whhel wells behind the molding. i just finished painting my truck and would like to still use the fender moulding. This seems to be a common rust area on these trucks.

 

Are you referring to the surface rust caused by the plastic wheel well flares scratching thru the paint? If so, one option is to use a clear film like the 3M film used for protecting the front of cars from stone chips, i.e. the clear bra. If you search Amazon's automotive category for "3M clear film", you can find it in bulk rolls for about $20.

To install, you would need to fit your wheel well flares to the truck and use a pencil or pinstriping tape to trace a line around the outside of the flare, about 1/8th inch beyond the edge, then remove the flare. Next, cut a 1/2" strip from the roll of bulk film and install it with the outer edge butted up to the line you made on the fender. Be sure to follow directions for installing the film, especially in regard to cleaning the paint surface. The film adhered to the paint will prevent the plastic from scratching the paint, and you won't notice it's there unless you get very close. You can cut the film narrower than a 1/2 inch if you want to make it easier to form a curve, but it's pretty flexible anyway.

Oh, if you just painted your truck, don't install the film or your flares for a while. Let the paint harden first; I'd give it a month or two.