So what do a sandbox and play dough have to do with Mulg? I used them both to finish his base.
I gathered the sand and glued it on to the base, carefully avoiding the areas that his feet were to be. After finishing all the gluing and painting, I set to painting the edge of the base. While doing so I noticed that the edge was very rough, it needed some serious filing.
I certainly didn't want to file it and re-prime the whole base so I whipped up some play dough. With it I covered the finished parts of the base. I filed off the pesky stuff, re-primed (while the finished rocks lay safely beneath play dough) and finished the edge.
Wallah!