Decided to make the air filter cover from fiberglass and used the moldless construction technique, where a foam core is shaped and the glass applied straight onto it. Summed up, the quality of a composite panel is directly proportional to the amount of labor and care used in preparation and lay-up. As always, vacuum-bagging would have made a huge difference, except that even if a pump was available, the foam’s so delicate it would’ve collapsed with 15 psi on it.
My possible mistake was wrapping the core in plastic to make it easier to separate from the hardened epoxy. That left an annoyingly flexible layer that kept moving around as the three layers of glass were applied, so the jury’s out. The wrinkles shown aren’t a big deal since they’re on the inside, and the part will be painted. The concern is that the loose plastic changed the radii of the curves enough to make it fail on the “good enough” scale, and we’ll know that tomorrow, which is also a back-to-work week. I should add that the last picture is of the part setting-up on a scrap piece of aluminum – it wasn’t layed-up directly onto the engine cover.