Try Liquid Rollers. its very good but costs a bit more .most boating store have it. Mine comes off the trailer like crazy for about 2 months...then its time to re apply. Silicone can build up over time and actually can get sticky, so ive heard, but ive used it and it does work, but not like Liquid Rollers Spray.
Trailer Parts Superstore - Liquid Rollers Bunk Spray Coating, 10 oz.