I've had pretty good results with vacuum resin infusion and a simple fiberglass rope around the perimeter - it's pretty tough and you can infuse it in one go. Your mileage may vary though
I think we're overthinking this. Pretty much any nut with at least 1mm of flange won't be pulled out from epoxy I sink it in, the only problem I see is bolt might get through the board, but it's easy to measure and safeguard against.
Sure, lengths need to measured carefully, but it's not exactly rocket science. I wouldn't do this on production boards for sure, but for test samples, this works just fine.
I got a few sets of those, which are SS316: http://www.junksupply.com/product/m6-snb-or-kite-insert-new/ But flanged nuts on both boards are holding just fine, and it's unlikely they'd get pulled any time soon, when properly seated in epoxy: https://www.aliexpress.com/item/Flange-nut-100PCS-M3-M4-M5...
You can check my thread, I faced similar challenges. If you're building a twintip though, I highly recommend using Airex C70-90 foam instead - it's much lighter (core weight difference was 400g vs 2kg WRC!), and easier to work with: 170x50cm board with WRC: http://www.kiteforum.com/viewtopic.php?f=1...
Warren @ easycomposites says the following regarding dry spots on the bottom: >Yes I suspect you are right that leaving the pump running caused the dry spots. Even with a resin break it can still dry out. When we infuse, we always ensure we have a leak tight bag as after the infusion, we turn off th...
re bubbles: I'm more or less convinced, that the dry spots were caused by me leaving the pump on for long time after injection - it simply sucked out some more resin than was required.
re soric: this actually looks like a good idea. I might buy some and try it out.