Its pretty involved and needs a bit of reveres thinking. To make the bit that goes into the snorkel i got a piece of pvc plumbing tubing that fits into the snorkle. Cut two small pieces of the pvc and bolted them to a block of wood. Waxed it and fiberglassed around it. That gives you the oval that fit into the snorkel. Then you take the pvc tube and bolt it to the outside at each end of the oval and fiberglass the underside of the tube and that gives you the revere profile. So now youve got an oval with what looks like two half circles at either end. Then you take a sheet of cardboard and measure out the top shape, transfer it to a sheet of polypropylene( the same stuff that Maccas food trays are made out of ) fiberglass that with a thin sheet so its still flexable. Positon the oval on the lid on the car in the correct height and positon and lightly fiberglass it together. Once thats done build the ramp that goes towards the gard, cut out the underside of the lid so it will feed air from the snorked and the proceed to build up the fibergass to the shape of where the gard and radiator support is.
Thats the simplified version of how its done
Easy ! Well not really ! Just time consuming !