Pot-pourrit of lessons learned from building my scarab22:

I will add to this as things come to my mind...

1. It si very hard and unpleasant to finish concave joints.(cockpit joints, beam fairings, beam stubs)
2. It is even worst to finish concave corners (beam stubs, beam to float joints))
3. Sanding fiberglass is not fun (whole boat...). Shaping solid fiberglass in even worst (beam UD)
4. Metering pumps for epoxy are excellent for small to medium batches. Graduated pots are best for large jobs.
5. Taping chines is slow. It is difficult to make constant radius chines. It is slow to fair.
6. It is very difficult to manipulate a float with beams attached. At least 3 people are required and you can't position it adequately for working on it. It also takes a lot of space in the shop. This is a MAJOR issue when you are trying to fair a float.
7. It works very well to glass the inside of a foam hull panel and glass the outside on the whole boat in one go. Tapes are used on the inside (no fairing). I made my centerhull like this and it is perfect. I would build the floats like this next time.
8. Float stringers (shelf) should be wood. Current design is very slow and not adapted. It should however be designed allow water to drain to the "bilge" of the float.UPDATE: The inside of the floats are always at 100% humidity. They are difficult to dry. There is always condensation inside so any wood in there would rot eventually, and it would be impossible to inspect. NO WOOD!!!
9. Beam stub fairings are the worst part of this boat. Their shape is awkward and it is very difficult to control the gap with the beam ends. Many clearance and fit issues. Plans are of no help there.
10. It is very hard to paint a cockpit without stepping in the paint!!
11. Aluminum parts are super: no paint, no maintenance, light, cheap.
12. Cockpit floor stiffener is not positioned correctly: it should be halfway between the traveller and the companionway. It should be positionned to support the weight of someone using the winches.
13. Folding geometry is questionable. During folding, there is a point where all pivots are aligned and motion is not controled. It works but should be improved. I used numerous plastic shims and pads to keep the folding and un-folding smooth. Also, the bushings are very sensitive to any play, so make them very tight!
14. Cabin space is very good and pleasant with the pop-top open, although when full of sails, cooler, gas stove, water bottles, and the top closed, it is good only for one small person.
15. Spray painting is difficult on vertical surfaces, but very easy on horizontal surfaces. The cockpit is very hard to spray paint correctly.
16. When spray painting, dust is not a real issue. It is easy and quick to clean the shop enough for the job.
17. When spray painting, LIGHTING is crucial. When you have your mask/goggles on, it is very difficult to see what you are doing. White paint on white paint is not evident, unless you can see a reflection off the surface, at any position on the boat.
18. Use a primer having the same color than the top coat, or very close. This way you will not be tempted to apply too much topcoat for coverage and runs will be avoided. (use white primer under a white topcoat...)
19. Do as much hull bottom work as possible while it is upside down. This includes waterline and primer as far close to the deck as possible. It is very hard to do when hull is upright.
20. The centerboard case is seriously weak as designed. Also, the drawings dont specify removal of  the core around the slot opening under the boat and calls for only one fiberglass ply. The loads from a centerboard are high and need to be reacted by substantial structure.
21. To assemble the boat, pin the folding struts on the centerhull first, then position the floats in the deployed position to receive the outboard pivot pins.
22. Have one beam detached from the floats or make 5th dummy beam to make the beam stub fairings, verify folding struts, position hold-down bolts.
23. Beams are about 6" too long to fit boat through a garage door.
24. To remove core for screwing fittings it is much better to use a hole saw from the inside than a bent nail from the outside. Just use the hole saw to make a nice round hole through the inner skin (1" diameter) for every screw, remove ALL the foam with a 1/2" sharp chisel and fill the cavity with putty. Laminate glass or carbon over the putty to restore the inner laminate plus extra plies acting as a backup plate. Then drill fastener holes from the outside.
25. Silicone sealant for bedding fittings or hatches is awfull. It sticks on everything and is slippery as hell, it smells bad and cures too quickly. Maybe very slow silicone is better. 5200 is very nice to work with but is very strong so dont use too much if you want to remove the fitting later.
26. Get a grinder with a cutting disk to cut ALL the fitting bolts and screws to the proper length. No fastener is the standard length!
27. When un-folding the boat, extend float that is away from the dock first and install the locking nuts by standing on the beams. Then extend the dockside float by standing on the dock and pushing the centerhull away. The tension in the trampoline makes everything smooth. To install the locking nuts, walk on the beams until your body weight pushes them down in the right position. I weigh 170 lbs and this is just enough.
28. Raise the mast only when the boat is deployed. If raising the mast with the boat folded you risk bending the shroud chainplates since they are not oriented to take side loads. If the chainplates were bolted to a bulkhead inside the floats (rotated 90°), this would not happen. It is possible to fold the boat with the mast up only if you rake the mast a lot to loosen the shrouds significantly.