I'm looking for a clear glossy coat to go over my epoxy/fibreglass acrylic painted waveski to provide a durable, UV protected, waterproof layer.

I have read somewhere that some people use marine varnish when making surfboards to finish them off as it's a lot cheaper (and easier) than automotive 2k lacquer.

Has anyone had any good experiences? I've found a few different varnishes on the net but not sure which would be best?:

1. Exterior Varnish.
Seems best for use outdoors being highly waterproof and durable, but not sure if it can be used on painted surfaces, only bare wood?
2. Polyurethane Varnish.
Very durable due to the elastic nature of the polyurethane, but not sure how waterproof or UV protective it is?
3. Yacht Varnish.
Designed for exterior wood on boats so UV protective, but again, not sure if you can use it on painted surfaces.

Most of the above work out about £10 a litre which is far cheaper than automotive lacquer which is coming out as £20 a litre for 1k, and £30 a litre for 2k lacquer.