Fusing Resin to Resin - need advice.

I've recently been making some alterations to my anime-style resin head base, which was first used to create Moriko: http://chikkennoodul.deviantart.com/gallery/?offset=48#/d5gyqr2

Part of this involved cutting away a lot of the excess cheek area from the mold, so subsequent heads will not look so wide.

But the main change I want to make is to my method for creating the bulbous 'dome' of the head, which is a necessary feature for this character style. For Moriko, I made the back of the head entirely from foam, which had a fair few disadvantages. Now, I'm wanting to cast the head domes in resin instead, resulting in a more lightweight, cooler fursuit head, not to mention a quicker production time.

So what I'll have is two parts to the head: the face, and the dome, both cast in resin. The challenge I'm facing is figuring out how to fuse the two halves. I'm assuming that no adhesive will work in this case, and so the resin itself would have to be heated up and fused together.

I already own a powerful heat gun, so that part is covered. What I'm hoping you guys can offer advice on, assuming I'm even on the right track here, is technique; how long to heat the resin, how to actually go about welding the two edges, and things like that.

Thanks for reading!