Okay, a little update.
I was going to make a whole new front end that was aero instead of trying to use the original front end. However, once the front was aero, the back did not match at all. I like the back end so I'm going with plan B but this is how I was working plan A.
I hot glued the fan-folded, thin, blue, polystyrene foam. This foam has writing on one side and a plastic film on the other. The film will keep the polyester resin off of the foam. Otherwise, it will dissolve the foam.
Any cuts will allow resin to contact the foam. The shiny side of duct tape will not stick to polyester resin.
The goal of this is not to make a finished part, but to quickly rough shape the plug for the mold to be made from. This one took about an hour. A final part made in this particular way would be very heavy once filler is added to smooth the contours. The polyiso foam used in the seat back doesn't bend at all. I would not have been able to make the curves without using a block of it and sanding them in.
Notice the many cuts in the foam. These allow the foam to make the twists and bends. The cuts should be made on the side facing out, using a sharp razor to cut approximately halfway through the foam. You need a box of razors from someplace like McMaster to do a project like this. A dull razor will not cut foam cleanly. I find it easy to do quickly with the razor held between the thumb and index finger where the razor's edge just protrudes past the fingernails. Pre-crack the foam at the cuts before placing on the form. For a compound curve, the cuts should be half way between the two bends (i.e. if the curve axis are perpendicular to each other, the cut would be at 45 degrees to either axis, basically an X).
In hindsight, I should have used 2" wide stringers parallel to the ground, then cut them at whatever angle necessary. The final shape would have been much better.
There is a sheet of painters plastic that was taped over the windscreen to prevent the resin from damaging it. I should have made a foam template to bolt to the windscreen mounts instead of leaving the windscreen inplace.
The white styrofoam block was against the front of the tire.
The fairing is very wide at the bottom for tire clearance when turning. Much of the bottom would have to be cut away for ground clearance when leaning. A separate fairing could have been made that bolts to the rigid fork tubes near the wheel. This would allow a very narrow, tire hugging fairing. FYI, the Helix uses a front trailing arm suspension with separate shocks.
The seat back was not vacuum bagged. It is two layers of polyiso and two layers of fiberglass. The complete seat back with piano hinge, latch, foam, upholstery, etc weighs 1 lb, according to my bathroom scale with me and the seat back versus just me. The tapering is performed with a rough razor cut, followed by very light sanding with drywall sanding screen to feather the edges and fully radius any corners. Glass does not go around 90 degree corners unless it is bagged. The glass is draped/stretched/fitted perfectly before any resin is applied. Then resin is gently applied with a 1" paint brush to keep from moving the glass around as it fills the weave. Only enough resin is applied to fill the weave. Anything extra adds weight. Any edges should wrap around atleast 2 inches or lay flat 2 inches past the last curve.
I use painters plastic on a table duct taped at the edges. I glassed the big piece first, with enough material to wrap around the back. Once I glassed one side, I carefully flipped it over, laying the wet glass on the plastic while I wetted out the wrap around. If you do any fiberglassing, get a box of latex gloves. A box of 100 is around $7. Put on a new pair everytime you are about to mix resin.
The strip of wood in the edge is a piece of plywood for the screws to bite into. The latch clip at the top is screwed into glass/foam only. It seems plenty strong enough for that, but I could route out that area and glass in a piece of wood flush with the surface. The surrounding area would need to be sanded until dull. The glass should extend out 2 inches all around. The wood and cavity would be wetted out with resin before sticking the wood into the cavity.
Prefit everything before picking up the resin. Regular scissors trim wet glass easily. Minimize over hangs, because the weight of them will lift the edges of the curing glass the moment you turn your back on it.
For polyester, use the least amount of catalyst to provide maximum time to apply all of the resin you've mixed and work the part. The only way to use the least amount of catalyst is to accurately measure the catalyst. Buy a bottle of MEK, not those tiny squeeze bottles. Veterinary syringes are perfect. They fit into the neck of the bottle. The catalyst (MEK) attacks the rubber plunger, tinting the mek in the bottle, but the cure is unaffected.
Velcro is very expensive. Buy "hook and loop" fasteners with adhesive backing by the roll. $11 for 25 yards of 1" hook and $11 for 25 yards of 1" loop is a good deal.
The adhesive sticks to the glass well. Sew the hooks to the vinyl, place the loops on the hooks, peel the plastic to expose the adhesive on the loops, then pull the vinyl tight and stick the loops onto the glass.
Be sure to use thread that is the same color as the material.
The windscreen mounts are 1/2" tube tacked in for now. The handle bar is 3/4". I used 1" dom because I had it laying around. I should have cut it length wise to make it 3/4. I may do that later. The flanges on the original bodywork had to be cut off because they were in the way.