Vaclavs epoxy tests make a good case for fill coats. If you always opened the compartments and never let them get steamed up in transit or storage I bet it woudn't matter. But that's a lot of discipline for saving a few ozs. How about brushing on a few ozs when the boat and epoxy are very warm or thin it with some lacquer thinner? Or don't worry about any possbible water stains and enjoy that boat weighing 4oz-16oz less.