Hi Andy,
I would use Epifanes U/V gloss varnish. We use it on all our full sized wooden racing yachts that we restore.
Not cheap by any means, but the most durable, deepest gloss single pack varnish there is on the market.
If you are going direct onto new untreated timber, it needs thinning down, approx 50 percent with epifanes brush thinners for the first coat. Following coats should be thinned slightly less, as a rule I normally add 20 percent, for the second and third ones, then 10 for the remaining coats.
To get the best results apply around 8 coats, lightly hand sanding with 320 grade abrasive between the final coats.
Apply it in a warm dust free area, it is slow drying, apply 1 coat by quality brush, allow 1 day to dry, lightly sand, remove dust, apply following coat and repeat sequence, allowing 1 drying day between each coat
Regards
Ian