Mike , I usually cover the plane first , then seal the firewall area with epoxy . overlaying the epoxy onto the edges of the covering seals the covering down as well as prevents fuel from getting under the covering . the firewall can then be masked off and painted with any dope or fuel proof paint you choose . If you you paint or seal the firewall prior to covering you may not get a good bond between the covering and the sealer/paint and the covering may pull loose