Right, test building has thrown up some issues.
I've constructed one of the central legs which went reasonably well, but, as with the Locust, I think some parts will work better as card and others as paper.
The Main body, however is a different matter. I think I over-egged the two main sections, creating a closed hull that another layer sits over, allowing me to add those lovely fin-like edges. All of this makes for compound errors though, that throw the angles out. It is, I think, a mistake to design parts that are intended to dove-tail because you can't account for paper/card thickness used by the end user.
Add to this that I broke the whole thing into three sections: front, mid and rear. In retrospect, that's just asking for trouble, like stacking three equally sized Lego bricks on top of each other.
I'm re-designing it now so that there is a single, long box that runs underneath for strength and straightness. The three sections will then sit on top. I've redone the front and rear sections so that they are no longer a closed hull but a bottom piece with a top piece that sits, umbrella-like over it.
I'll test-build it over the weekend and see how it works.
I'm also, hopefully going to test-build the fiddly gun pieces :/
Crow