Did this project couple of weeks ago and wanted to share if anyone is interested in DIY rock guard. I put Herculiner on the bottom door panels and painted it for around 65.00 compared to 600.00 at line x. I think prep is key and sanding enough to get a good working surface. I used 2 coats of Herculiner. I bought 2 inch foam rollers at Lowe's to apply the Herculiner and Denatured Alcohol to clean the crap out of the surface prior to putting on the Herculiner. 20 minutes after the last coat of Herculiner pull the tape off or it will be a PITA to get the tape off! Let the Herculiner dry overnite and painted it the next day, it did stay tacky for about a week so no car washing.