SIPs for TF enclosures typically lack the same amount of structrual elements. They will have significantly more plywood splines and less dimensional lumber. We pay about 1.00 per sq. ft less for the SIPS used on TF vs the strucural SIPS.
As far as the OSB getting wet is concerned. Thats more a problem of building practices. There isn't a good reason why SIPS or any wall structure should get wet from external sources. My guess is.. It will last at least as long a traditional 2x6 wall with the exact same OSB exterior sheathing.
More than likely if they were installed correctly they will last longer since they are less likely experience the same types of leaks and condensation/melting frost running down the inside of the OSB of a traditional wall.
At the end of the day... there are only two kinds of SIPS. The ones that got installed right and the ones that didn't.
