I have had great succes with Testors Clear Lacquers, dull and gloss, in the spray can. I have sprayed it on top of enamels, lacquers, and acrylics with no problems. Take your time and build up the coats slowly and always make sure the paint you use is fully cured. I always give it a quick wiff to see if i can still smell the paint. If you cant smell the paint anymore you're golden. enamels take forever to fully cure. i have waited up to a month for some enamels to fully cure. thats why i primarily use acrylics and lacquers as they cure in a day or two depending on your climate. Testors Model Master Acrylics brush paint really nice as well as the Vallejo line of model paints.

hope this helps

peace out