I grew up at my Dads body shop and learned to paint there with no paint both, spraying enamals, lacquers, and urathane paints. in the winter we would paint in the early afternoon when the shop was warmest and in the summer we would paint in the evening when the shop was coolest. This was southern MD where the humidity was regurlerly above 80%. If you see moisture condinsing in the evening, all that water came out of the air lowering the humidity. Good water traps will keep it out of the lines and an additional measure we used to take was to run a section of the coiled hose through a cooler full of ice in between the line coming the compressor and the line to the paint gun (we had air lines hard piped along the walls). The ice in the cooler would condense any remaining moisture out of the air and also keep the beer cold. We never had issues with moisture when we did this. As far as off gasing or evaportion causing problems with the paint after its sprayed I think matching the temp range of your reducers or using additives to slow it down will help but I haven't painted a 1/1 car in over 10 years so I'm not sure what additives are available these days. I have had some fogging of spray paints when spraying in high humidity but I can't really control the mix in a spray can. I suspect your correct that the paint was starting to flash off too soon on your second coat, if the humidity was high the temp was high and that would accelerate the catylist in the clear.