I wetted out a single layer of 6oz. fiberglass cloth and draped it over the masking tape. Once it cured, I picked all the masking tape off and test-fit it on the engine. Not too bad for a place to start. Don't worry, even though it looks wet, this cloth was cured before I draped it on my unprotected engine!

I needed to stiffen up the single layer of cloth so I started slathering Bondo over the fiberglass. It actually worked pretty well.

The Bondo was pretty tough to sand and I couldn't get it as smooth as I'd like it so I decided to try plaster over the top of the Bondo. It ended up going on pretty smooth, but it was a bugger to sand.

In a final attempt to achieve a smooth surface, I applied a thin layer of modeling clay over the plaster. I worked it smooth until I was tired of messing with it and then applied PVA mold release to the clay.

I covered the clay with 4 layers of 6oz. cloth and then a layer of peel-ply to save a little sanding later.

One of the things I learned from a friend when working on my gas tank is that the compound corners lay down a lot better if you cut fiberglass cloth on the bias (on a 45 degree angle to the weave). This was much easier to lay down and poke into the corners than anything else I've worked with so far.

The plenum is out of the mold and has been rough-cut to fit the aluminum sides. Looking pretty good so far...