I have always applied varnish within a day or two of the final coat of epoxy...without problems. This said, I generally refinish my boats after two or three years of use due to scratches, cracks, gouges and what-nots. I also reapply varnish coats after only 24-hrs, assuming warm conditions, be it a hot day or a heated garage. I have always worked with SPAR varnish since that is what Donnie at Waters Dancing keeps selling me. I get a discount so I get what I get.

All that said, why would you varnish the inside of your boat anyway? If it's coated with epoxy it has all the protection it needs. Varnish is usually applied for UV protection and you don't get UV exposure inside the cockpit unless you store it outside and uncovered. Just wondering, eh!

Robert N Pruden