I've done ~a lot~ of this, and it's easy, but you have to be absolutely methodical and you cannot cut any corners. Obtain real mold release wax and real mold release compound, modeling clay (plasticine)tooling gel coat, light cloth, mat, resin, cups, sticks, release wedges, gloves, acetone, lacquer thinner, and lots of paper towel.
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Clean and buff the panel very well and apply 3 or 5 coats of release wax. I'm not kidding. It doesn't take long and you won't regret it. Cut out all the pieces of mat you'll need to end up w/ about 1/4" thick layup. For stiffening I use pieces of mailing tube split in half on a band saw, or wood - 1x1, 1x2. If the mold has "sides", you'll form dams with lots of modeling clay, lay up the mold over these dams, then removed them, wax and release the inside of the mold you just made and repeat the gelcoat and layup on the side of the part and onto the adjoining mold. Drill holes for 1/4" bolts before releasing the mold sections from the part.
Apply a coat of mold release - I used to spray it but I usually use a pad made of old, soft T shirt and gently rub on a light, wet coat. let it dry.
Mix your tooling gel coat and using a wide, cheap "chip brush" lay on a thick, wet coat. You want a film thickness of 1/32", maybe more. Thick! The gelcoat is what picks up the fine detail and makes a hard, durable inner mold surface.
As soon as the gelcoat is cured you can begin laying up mat and resin. I usually put out a line of 10 oz paper cups of resin and use a hardener dispenser so I mix a cup, which only takes a minute, pour, roll w/ a laminating roller, dab w/ chip brushes into corners and around edges, and when the cup is mostly empty, catalyze the next one and work continuously.
(Laminating a 5 x 7 foot tail section for a race car takes hours and resin kicks in 10-15 minutes tops)
It is critical that the lamination to the gelcoat has no voids or bubbles! NONE!
I'd probably let the first layer set up most of the way before continuing to avoid heat buildup induced distortion from a thick laminate's exothermic reaction.
Once cured, use a jig saw and cutoff wheel to trim most of the excess around the perimeter. Then start with the wedges at a corner - usually a couple wedges and the mold just pops of easily.
I've had a whole car nose exit the mold with a wee tug. It's all in the prep.
A good book on the basics: Composites: Aird
