Here is a fiberglass cowl I'm making now.
Click on any picture to see it big time.
Here is my current project.  This will
be a fiberglass cowl for my Hobbico
Avistar 40 with a side mounted O.S.
.40 SF.  I've built this so far using the
lost foam methed using West Systems
Epoxy by Gougeon Brothers.
My project is stricly a home brew bit I think it is
typical of how it is done.  I have never done any
fiberglass work like this other than glassing the center
section of a wing but I think it turned out terrific so far.
 Right now I'm at the point of getting ready to prime
and paint.  I'll explain what I've done so far.  I used
the lost foam method.  First you find a piece of very
closed cell foam.  I found mine at work, it was several
small sheets of foam for box packaging that I contact
cemented together.  You then cut out the desired
shape you need.  A hot wire system works best but I
don't have one so I just cut it out with a coping saw
and sanded to shape.
You then coat the mold with a very light mist of 3M
77 contact cement and lay down strips of 6 oz.
fiberglass cloth.  My mold was basically square with
rounded edges and a slope to the front.  I used four
strips, one for each side.  The contact cement holds it
down and keeps the frayed ends from becoming a
nuisance.  I mixed up 30 grams of fiberglass.  25
grams resin and 5 grams hardener.  Brush it on
working it into the weave.  Soak up any excess with
toilet paper.  Do that three times then follow up with
one more coat of just fiberglass resin/hardener for a
gel coat.  Then, and this is the cool part, you pour a
little gasoline into the back, onto the foam.  The
gasoline just melts the foam away and you are left with
a solid fiberglass piece.  I then used my Dremel with
1/8 router bit to cut out the engine, carburetor &
muffler clearancess and nose hole.  Mine came out a
little oversized at the fuse joint.  Maybe 1/8 all around.
 I'm calling this an air exit for the engine cooling  Better
excuse than making a new one.  It is a lot of work but
it's fun.  I think West Systems Epoxy is the best.
RC Hobby Guys
Avistar 40 Cowl