David, those shipping containers get real hot in the summer time. I have loaded/unloaded hundreds of them over the last 30 years and the temps get way up there.
We warehouse a lot of the spray foam products and it does work very well, but....once the interior gets warm isn't it still going to be pretty hot?
Have you considered building a pole barn type roof over your container? That might be a cheaper solution and also allow for creating some vents in the container.
Just my 2 cents worth of opinion.
