Solve my chemistry problem and I will pay $75!!!

Hello, I am looking to thin the viscosity of polyester gel coat. I am looking to thin 40%-50%. This is so I can spray it with a hvlp turbine sprayer. Currently I am using MEK as my thinning solvent but it is affecting the curing of the polyester gel coat.  I am using MEKP as my Hardner/Catalyst. The manufacture recommends only thinning up to 10-15% with styrene (thinning solvent) or MEK but it's still to thick to spray with the type of equipment I need to use. I know I can use acetone, laquer thinner, MEK, N-butyl acetate.  I don't know if I should use a blend of these or use something totally different. Im not that educated with chemistry, I'm just an over educated painter. I own my own bathtub resurfacing business and hope I can get this coating to work! Thanks and hope to hear from you soon!!! Cheers, Matthew :)