Stress and strain on fiberglass
I will not suggest that I'm an expert. That said, there are a few observations I would like to make. There is an engineering term called "elastic limit". It discribes the maximum amount of stress and strain a material can withstand before it deforms and cannot return to it's original shape. Just saying "Oh, it has a dent, the fiberglass is distroyed", is not accurate. The real question is how deep and over what size area. I too, have the dent issue. I intend to tune my trailer to eliminate the dents. Am I concerned? Of course. I will tap the area carefully to listen for dead spots. After that, if it sounds tight, I will not worry about it. Fiberglass doesn't break like glass. A Corvette has fiberglass suspention. A fiberglass spar is used to hold up the entire rear of the car. If you have a dent less than 3/8 inch, over an area about 2 1/2 feet wide, you probably don't have a problem. That would be the max depth and minimum area. Tap your hull with the butt of a screwdriver in a non-dented area. Get an ear for the sound. Then go to the dented area, after the dent is releived, and tap that area. Same/same? no problem. Softer, dead sound... problem. It's not hard to see for yourself. Now the other side of the queston. Gelcoat. As far as I know, no-one uses gelcoat for automotive suspention! There maybe micro cracks in the gelcoat. Those are the ones I would be concerned about. At the very least I would think about some sort of sealing process being applied to the area, wax at least, perhaps paint. The prospect of blisters is a grim one. Stressed gelcoat below the waterline on a 20+ year old boat that will see many months in the water is an issue. If you put the boat in for two days, then leave it out for a month, perhaps less of an issue. You said you are going to eventually paint the hull? A little gel coat repair during the paint-prep stage is not much work. I say, float it and don't worry. Watch the area, and plan a paint job in a year or three. Just my .02 .