When I was in Canada, I picked up a small bottle of Mod Podge. It's a glue I'd read good things about in American Magazines, but had never seen for sale in the UK.
I'm not sure what's in it, but it looks like PVA but dries perfectly matt. Using it for sticking details on to a couple of dioramas recently, I was really impressed with its invisibility when dry. The grab is quick, so not too much propping up is required either.
Obviously, I hadn't been paying attention as you can buy the stuff in craft shops and Hobbycraft. In fact there is a whole range of them to play with, so I've acquired a new, big bottle and some antique finish stuff to play around with.
First, I need to read the ModPodgerRocks blog.
Update: Early readers will have spotted that despite being written on the bottle in large, easy to read letters, I insist on call this stuff Modge Podge. I've updated the blog, correcting my brain isn't quite so easy.