paint problem

I have a problem with the paint staying on the fenders of my trailer. We travel around 4 miles of gravel roads to get to our honey hole. We have sanded down the remaining paint on our trailer primered with rustoleum and repainted once, but we cant get the paint to stay. I would love to have my trailer galvanized but unsure on the cost to benifit. Anyone have any problems with trailer paint and solutions to the problem?

You could try cans of spray on bed liner.

My fenders are getting dinged something awful and I don't even drive down any gravel for any length.

Spray liner as ben suggested may work or you can always add a set of mud flaps to the back of your vehicle.

For now, I'm just going to have to keep after mine with the gloss black touchup paint.