If the rust spots are evenly spaced, you can use surface stitches to cover them. Good stitches might be Smyrna cross stitch, satin-stitch heart, queen stitch, satin stitch lozenges/triangles, palestrina knots, etc. If the spots are not evenly spaced, balance the design by adding extra stitches between the spots.
Fortunately, most states require drivers to equip their trailers with brakes and devices known as brake controllers. When a driver presses on the brake pedal in his truck, the brake controller lets the trailer's brake system know how much braking power is needed to stop the trailer.
But if you're going to be part of the population that is pulling a trailer make sure you put safety first. Many new cars and trucks come with towing packages, but most do not come with a Trailer Brake Control. The Trailer Brake Control is a module that controls the electric brakes found on many trailers.