Jim,
We used spray foam on a lot of our buildings at Ft Eustis before I retired from there and it is realatively cheap quick to appy if you have the right company do it for you. Not only does it make the building look better but it increases the insulation value of your interior/roof and will also seal up existing leaks. The only thing that was required was the surface to be clean and dry and can come with a 10 year warranty with depending on the company an additional 10 year warranty with nothing more than a good inspection at the 10 year point of installation.
Just my .02 worth
Darrin