No I haven't tried that product, let me know how you make out with it. The trailer is boxed material meaning it isn't three sided. I know it isn't water tight because the tongue is removable and if you get it down in the water enough, the trailer would fill with water and there are only a few tiny drain holes. Personally, I see the design as flawed. When I get the boat off the trailer, I am planning on drilling holes in the bottom in several locations to make sure water has a way out if it gets in. My guess is that is how that spot rusted anyway. Hard to tell if there is a bunch of rust in that particular area. My buddy said we can just cut out the bad, make a new steel piece in the shop and weld it up. The side guides, yes, they are useless in my opinion where they are, the step is blocked. Once I get the bottom side adjusted and done the way I want, I will address the position of those. Done correctly, they could enable my wife to put the boat on the trailer.....well, maybe not but you know what I'm saying.
Rich