Dean,
I'll tip in albeit late..........
I use (by Airbrush) Model Master Acryl #4637 Semi Gloss Clear or the Flat version, #4636 thinned about 1part thinner to 3 parts Clear. It has never let me down, dries quickly, and I have some 10 year (at least) old finishes here that are still in excellent condition. It's the final coat after Future followed by decals however I weather after the Clear overcoat. Just another option to consider, works well for me. Use only the Acryl Thinner specified BTW.
Cheers,
Lance