Cellulose paint, problems with blooming

I have been having trouble with the black cellulose paint I am painting my Range Rover with blooming. I am using antibloom thinners. What is the highest safe relative humidity to be spraying celly paint in a garage? Are there any ways to prevent blooming or to lower the humidity other than waiting for a perfectlty hot, dry & sunny day? Sorry if this is a little off topic but there seem to be some experienced painters who read this group I remember from previous posts. Thanks, Fergus