This board was done without a mould, so basically you just shape the core material to the design you want, and then cover with the fibres (glass, kevlar, and carbon in this case). Spray-glue helps to keep the fabrics attached while working. After the reinforcements comes the peel-ply which distributes the air/resin, and then it all goes into the vacuum bag.

The bag needs to be sealed air-tight, and if you have sharp plastic tubes or other stuff inside you need to carefully look out for leaks while the resin is curing.

that's it, shouldn't be too hard if you've just got the energy and enthusiasm to experiment a bit!