My understanding is that it is not a good idea to thin epxoy. The out gassing of the thinner during curing creates micro pores through the epoxy jeopardizing the water proofness of the epoxy or in this case the sealing of the wood. The whole idea of a seal coat before glassing is to avoid starving the glass of epoxy during the next coat and to prevent bubbles comming out of the wood.

Put a thin even coat of epoxy on the wood using a roller and allow it to cure during falling temperatures to draw the epoxy into the wood. When you pour the epoxy directly on the immediately spread it with the roller. Where it is allowed to pool or run and soak in for a while before spreading will show up as dark spots on the finished boat. I use Raka epoxy it is quite thin and I have used EpoxySheild from Glen-L it is quite thick. Night time applied seal coats without thinning worked fine with both.