Advice please - finishing laminated beams

I helped a friend put on an addition to his house this winter which features exposed laminated wooden beams. They are only decorative in this application. They run throughout the addition and in several places, they go through and stick outside about 5 feet. We installed these beams in December and obviously we need to get some sort of finish on at least the exterior portions soon.
I was thinking that using Minwax spar urethane would be the ticket for this application on both the exterior portions and interior. Does this sound like the right product to use? Any better suggestions?
I consulted the Minwax website and looked at the instructions for their spar urethane but it doesn't give a minumum temperature required for application. I would assume that we would have to wait until the temperature around here (Michigan) gets at least 55 degrees before we could apply this finish. I do want to get the exterior portions finished before the spring rains come. Any ideas?
Thanks for any comments on the subject.
Frank
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I've had some spectacular failures with that stuff - probably due to the sun exposure. Please check out the Sikkens lineup before you coat.
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