I have a requirement to apply a clear finish over a model yacht moulding in pre-preg.

In short, the moulding is in 1k carbon cloth, and the surface finish is not perfect by some margin. The strength, quality, and accuracy of the moulding is fine.... but the aesthetic finish is poorer than it should be.

The mouldings are exposed to sunlight from time to time, not on a daily basis, maybe a couple of days a week at the best. Some will be in hot countries with intense sunlight though.
They will not be exposed to significant scratching, unless rough handling or accident occurs. They will be placed in water for short periods, sea and river/lake (model yachts!).

So what I am looking for is a clear finish that can be flatted and buffed up to an excellent finish, that has some degree of UV stabilisation, is temporarily saline resistant, has a degree of scratch-resistance(although not essential) and forms a good bond with the pre-preg(assuming it's properly keyed).

My thoughts turn to a quality automotive 2k polyurethane clear coat.

But has anyone any experience of this? Or are there other alternatives?

Depending on how much you will need to "even out" the surface, it will be a choice between 2-comp polyurethane or thicker layers of UV resistant Epoxy ..
However .. Epoxy will not polish up to a perfect "mirror finish"  .. so if yo do need a level of "filling" go for both.. First a layer of coating epoxy -- flatten that out, get a good even surface, then 2-comp clear coat.

That way you will get a perfect and very durable finish ..

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There is really very little levelling to do. It's more the case that the surface finish is blotchy looking, from a kind of print through effect. It's more that the centre portions of the weave are more "fibrous" in appearance than the hollows adjoining, which are a little more resin-rich.
What resin there is on the surface doesn't take much to flat through, and doesn't buff up at all.

I was leaning towards 2k PU Automotive, but wondered if there was a epoxy-specific product that was uised to good effect.

My only area of concern is adhesion on edges. The openings on the deck are covered with sticky backed waterproof fabric to create a water-tight hold, and they do need to be removed from time to time. As long as the adhesion between the 2k PU and the pre-preg is enough to withstand repeated peel-offs then I'd be happy.

I find epoxy coating is not so good as other techniques. It can be very sensitive to surface contamination (fish eyes) and is then also very hard to sand.