I shaped the timber and the top of the melamine to the curve of the plenum top with the linisher, sanded smooth, waxed a few times, applied PVA agent and let everything dry. They I layed up lots of small bits of glass, adding the flanged tube after three layers. When everything was glassed, I iced the top with a mix of epoxy and Aerosil 200 filler so that I can sand the flange smooth to get a good seal with the plenum top (RTV will help there too). I don't mind extra epoxy collecting in the bottom, as this will help me smooth the lining and make it easier to remove residual oil with a cleaning rag.
