I've now sprayed the Matt coat on the model and think I've found my new favourite Matt varnish. After reading some favourable reviews I bought a bottle of AK interactive ultra matte varnish, AK 183 to see how it would perform. In a word brilliantly, after a vigorous shaking of the bottle I plonked some in the airbrush and voila! Perfectly flat almost instantly. It certainly out performs my usual varnish and does not mask the fine detail or weathering effects added previously, in fact i think it enhances them.
I've also painted the figure using various Vallejo colours and I'm very pleased with how the splinter parka turned out. All that's left to do now is add loads of mud and dust to the lower hull and sort out a base.