Scrubbed the spars and inside of the skins with a maroon SB pad and EcoEtch … about 5 mins each and then rinsed. Primed the inside of the skins and spar channels with AFS primer, thinned a bit to about 20 sec M50, 15 PSI at the gun. Found that a few light passes are best, otherwise the primer is too thick and runs down vertical surfaces and dries in a ridge or bump. Be sure to let the primer dry at least 12 hours before flipping, othwise you risk the primer sticking to the supports. Patience pays off here.