Make sure to buy really good magnets. I think they are rare earth magnets or something like that? They need to grip the mag so hard that it will not fall off while running. Mags get pretty heavy. I have a DAA magnet that the only way to get my STI mags off is to pull them straight up. You can't just pull them off easily. That type of magnet might cost a little more.And yes, you need to cover it when not in use. A buddy turned me on to a thick rubber pipe cap from Lowe's. Everything will stick to the danged thing if you don't keep it covered well. Scratches the hell out of your truck too!