I would glass both halves separately but avoid the top edge where they would join together, once both are cured do a layer of gelcoat along the seam and squish them tight. You will probably have to do a skin of polyurethane inside to give some strength to the unglassed gelcoat section.
I’ve done a few bumpers the same way, they come out extremely strong and lightweight because tey aren’t solid resin.
Lawrence
Sinny don’t worry, the goal here is to ship the throwers with both halves bonded and cleaned 
(oh but PLEASE buy yourself a dremel. Every prop builder should have one!)
Thanks Lawrence, thats pretty much the idea I had too. Ill hopefully have another pull done today.
Understood 
I’ll get one soon.
Rock on! How light is that thing? The first couple pulls from mine were like 2lbs if that.
Pretty damn light! It’s weird picking up a thrower and have it weigh next to nothing.
UPDATE! Great news guys, the idea I had and the method lawrence explained worked great! Pulled a fully joined thrower out of the mould today!
One small issue im having though is that the gelcoat remains tacky for quite a while. The test pull I cast on thursday is still tacky. Ive spoken to a friend and he said keeping the parts in the mould overnight, wrapping it in a binbag for a few days and adding more catylyst to the gelcoat all help it cure. Ill make one more test pull using these ideas and if its still no good I may have to switch resins.
Sorry for the slight delays guys but I want these to be the best I can make and being the 1st time ive ever done any major fiberglassing I need to get the techniques down as best as I can. Thankyou all for your patience
With gelcoat you’re probably using an MEKP catalyst? You could try filling a spray bottle with MEKP and spritzing the tacky spots. That should cure it within a few minutes (just don’t get that crap on your hands because it burns like a sonuva…)
You’ll probably want to wipe it down after as well
I saw a vid on YouTube where a guy was dusting it down with powder to stop it being tacky… Would that work?
Can’t wait to get this bad boy in the post!!!
It will be tacky for a few days after it comes from the mould. If you want to stop the tackiness right away you can give it a rub with some fine steel wool. Powdering would also work, but these methods will change the surface finish slightly.
I don’t know if a wax coating would work, wax is supposed to be added to gelcoat if it’s being used as an outer coat so that it isn’t tacky BUT it wouldn’t work when using a mould, as the wax floats to the surface and would be on the side where you need to lay glass. Maybe an after coat of wax might help? I’ve not tried this method.
If should stop being tacky after a few days though…
Lawrence
Thankyou for all the help guys!
Ok heres a quick photo of the latest pull. This one was joined together in-mould and then I shot a layer of primer over it to show details better. Another step closer guys. Just gelcoated up the mould again and then ill get to work on glassing another, hopefully this one will come out perfect.
That is bang on!
FBO!
Surprised there’s still a slot left for ordering one. You’ve inspired me to finish my project. 
They look really awesome. Very very clean. Well done.
Thanks fellas! New thrower’s looking even better. Hopefully wont be much longer before these start shipping.
That looks absolutely amazing Nick!! Great job!
Thanks! Ill be pulling the 3rd cast today so hopefully this one will be perfect
Oh and I also did a quick build up of the 2nd “almost perfect” cast to see how it all looks when (roughly) put together. I also know now which areas need special attention and reinforcement. Ill get a photo up of that too.
Ok while I have the latest thrower curing in the mould i snapped a quick photo of the latest “reject” pull after a VERY quick build and paintup. I put this together in about 90 minutes.
It looks great, I’ll take it