I've had good luck with 3M 101 Sulfite (formerly Thiokol). It is easy, but messy, to take off before it dries (use turpentine/mineral spirits), and not difficult to rub off places where it is not meant to be when dry.

The problem I have with Boatlife products is that they are combination products and I really don't know what I am putting on.

As for the 5200 polyurethane products, they do take the gel coat off when hardware is removed or replaced - first hand experience. The Silicone products can not be painted over, and, I am told, where it has dripped, even if cleaned off, still can not be painted over. Bad news. However, if you mask off the area, silicone might be the answer. It is very waterproof, cheap, and pulls off easily when replacing fittings or resetting them (However, you can not put a second coat on). Otherwise, I would suggest you try the 3M products (I do not own stock in the company or work for them).

The problems you reference may be because Boatlife products are combinations - so, for example, you have the problems with silicone and sulfite- or with silicone and polyurethane (whatever the mixtures are). I don't know.