After working with V color on my first couple figs I am toying with the idea of working outside my only concern is spraying in the heat and humidity. Is this a valid concern, will I run into problems?

Unless you can visibly see moisture beading up on the surface of your figure, I think you'll be okay... the force of the air coming from your airbrush should probably be sufficient to push any moisture away for the paint to stick. Paul recommends that you have your air pressure set around 30psi and he sprays outside, but you may want to test it on something first, just to be sure.