Thin your first coat of varnish atleast 1:1 with minearal spirits or
turpentine. This will help the first coat penetrate the wood better.
Especially on end grain. I generally add some tung oil or boiled
linseed oil into this first coat also. You can apply subsuquent coats
straight but I prefer to thin them some also. Many thin coats last a
lot better than a couple of thick coats in my opinion.

It is a good thing you built the bench to last forever because Spar
Varnish takes forever to dry ;-).