Not really a resin question, more of a Gelcoat question.  Would the above Gelcoat be suitable for taccing my outer layer into my female mould?  The mould is a tube, 300mm dia 1500mm long, and I am wondering how to secure the cloth into the roof of the mould without it collapsing.  Subsequent layers, peel ply infusion mesh etc. can be secured with spray adhesive I think?  Is there a better way?

Don't go down the sprayed acetone route, as the formula of the GC50 has changed since the bonnet video was made, in order to extend the time that the hardened coating can be laminated onto and still adhere well, so acetone will now cause cosmetic problems

If applied by hand over a mould prepared with a chemical release agent, GC50 also tends to fish-eye a bit, so spraying is usually the best option. Not certain how it'd behave when rollered, but it doesn't get overly tacky when nearing it's hardened state. I don't honestly think that it'll work very well in terms of holding onto the surface layer fabric, even if you can accurately determine its optimum state of cure.  

Your idea sounds quite tricky to pull off and I can't quite picture how things will be held in place inbetween removing the bindings and getting the bag sealed and pulled down, but perhaps I'm not imagining things correctly?

However, a spray tack like Aerofix 3 would work really well, I'm sure, even over quite a large surface area. I briefly tried Aerofix 2 some time ago and that seemed more powerful still, but I don't think that it would be quite so good in terms of not showing itself on the surface of the finished part, as it felt a little more 'heavy duty' and less refined. I get through a lot of the Aerofix 3 and, combined with using GC50 sprayed into moulds beforehand, there's never any visible traces. If things don't quite go well, it does allow you to remove the fabric again quite cleanly, as the tackiness of the spray wears off after while.