All good advice.

Side cutting bits fly through the fiberglass like a hot knife in butter, so they can easily get away from you... but they are wonderful when removing large areas.

Dremels with sanding drums & wheels permit finer control.

Always work slowly. Refit and test, then cut, rinse, lather, and repeat...

It's taken me as long as 3-4 hours to do a more complex cowl, but the end result is that people often ask me how I get everything cut so close and neatly.


A minor tip...

Once you've started an opening or hole, and are nearing the final sanding, apply thin CA to the inside of the cowl around the area that you are working on.

This will prevent cracking and help to strengthen the areas you are cutting into. It will also eliminate fiberglass "hairs" in the cut out areas.