Scott-S6 wrote:Varnish after the sand and flock is a great idea - it locks the sand and flock in much better.
Agreed. I dip using Minwax and I varnish after the flock/foliage/etc now (didn't used to) and it really helps to keep things in place.
As for the PVA, I've found it sticks pretty well as long as you seal it with matte spray afterwards. If you're using sand, you can also use a very thin layer of thicks superglue, but that's problematic because sometimes you end up seing the glue marks after it dries.
If you're still worried about the PVA sticking, paint over the base with Gesso, then glue on top of that. Gesso will also give you nice "tooth" so that whatever paint you use on the edges of the base will adhere well.