Like Scott, I put a bead of proseal under some plastic cling wrap (like Saran Wrap) and screwed down the panels, through the plastic wrap, and let it set up for a few days. Then unscrewed the panels, peeled off the plastic wrap and let the proseal cure some more. Seems to work fine as a gasket. I used proseal rather than RTV or similar because 1) I had it around; and 2) I figured if some got onto the skin it would not make the skin unpaintable (whereas the RTV apparently causes all sorts of problems).
Cheers
greg