A surprising three coats went onto the interior walls. We used a product called Aqua-Prime, which we also used on the roof, with a ceramic bead additive that provides excellent insulating properties. We’re fairly confident that this step, along with the RocWool insulation that will be added later, will have been worth the effort. Not only does it provide extra sealing to the seams, but it also will help us stay cool in the southern sun. This is a metal hot box, after all.