After a couple iterations of "almost right" on the panels for the 4ft. wide trailer, we ended up with two pretty much perfect panels for the 5ft. - not that there's a structural difference, but "perfect is perfect"...
The basic method:
Dry fit panels in form by aligning and clamping the top edge and forcing the curves to lay down. Bear in mind we're using two layers of 1/4" core for flexibility.
Cut the bottom edge so that the panels are in line when in the form - they won't be when they're flat.
Lay the panels out on top of a cardboard sheet, cut the fiberglass, peel ply, and breather to fit and set them aside.
Cut the bag the size of the form (or a little bigger).
Apply seal tape around the form perimeter.
Align the bag and seal the top edge into place - leave the backer on the rest of the seal tape.
Roll up the bag and flip it over the top of the form and out of the way.
Apply epoxy to bottom (outside)sheet of core.
Lay top (inside) sheet of core onto bottom sheet, align very carefully at the top edge.
Lay fiberglass onto dry top sheet of core.
Roll epoxy to saturate the core veil and the layer of fiberglass.
Lay peel ply onto fiberglass - overlap sides by a couple inches wherever you can.
Lay breather onto peel ply. Don't overlap as much with breather - it wants to be removed along with the peel ply, not separately adhered.
Tape the top and bottom edges of the breather around the ends of the stack and onto the bottom layer of core in 3-5 places at each end - it keeps the breather from falling as you bag the stack.
Breathe yourself for a few minutes - if you picked the right resin you now have ca. 30-45 minutes open time to get things under vacuum.
Back to fun!
Put three spring clamps onto the top edge of the stack - these will keep the sheets from shifting against each other as you move the stack into the mold.
With assistance, move the stack. Align the top edge with your witness marks on the mold, and transfer the three clamps to clamp the stack to the mold, through the top edge of the vacuum bag.
Help your assistant to make sure the bottom edge of the mold is aligned with the witness marks and that the top and bottom sheets of core are aligned.
Go to the bottom of the mold, and while your assistant pushes on the bottom edge of the stack to keep it forced into the mold place a few spring clamps to keep it in place.
Seal the vacuum bag down the mold edges, leaving enough bagginess in the middle so you're not stretching the bag too much.
As you seal the bag across the bottom, remove and replace the spring clamps in about the same places.
Pull yourself a nice little vacuum.
Find and fix the leaks.
Go have a nice beverage.
Sleep.
Come back the next morning, pop the vacuuum, remove the bag, and peel off the breather and peel ply.
The core should be stable in the form you've pulled it into, but still a bit flexy - it will stiffen completely when you skin the outside of the trailer.
And now, the pictures!
Pallet o' Plascore! Hint: Build four or five if you're doing this - the pallet weighed twice what the core does. Spread the freight cost among friends...
My photogenic side. Please use the method in the text and ignore what the man in the photo is doing - this was the first panel, which we are glad worked as well as it did.
See? It turned out sorta curvy and "back-of-TD" shaped!
Say "Hello" to my little friend... This is a spendy but VERY versatile vacuum pump, with both regulated and "always on" modes. Down here where it's 85F at night you need a blower running to keep it cool (has a thermal cutout) while it runs overnight for you.
These are the Front and Rear panels for the 5ft. trailer - by this time we were practiced enough to pull down two at once. Note the PVC pipe across the Rear form - it holds the sharp curve into the form during setup and bag placement (and means you only need *one* assistant), and ensures that if you somehow lose vacuum before the epoxy cures you won't have to rebuild the part - the sharp curve will still be there.
And here's what the 4ft. panels look like when they're out of the mold and freestanding.