Personally, I would have no qualms with using Smartside Panel without an OSB sheathing. It is rated for installation with or without. I have installed this product many times and I do like it. You do need to check with your local code office about the use of sheathing as well as vapor barrier placement. The siding panels, like most siding products, does require a breathable moisture barrier behind the siding. Some areas will also require a vapor barrier on the inside wall.
Be sure to to seal all edges, especially the bottom, before installation. Don't leave cut unprotected edges near windows and doors etc. I would use Ame's Super Primer for the edges, but paint should work. I would even seal the edges that will be caulked as the caulk will stick to the Ame's primer much better than to the primed panel. Ame's sells water proofing paints too. Be sure to follow all installation instructions, which are basically the same as other siding products, such as, expansion gaps, off of the ground, nail patterns, etc. Here are the install instructions. http://www.lpcorp.com/WorkArea/Download ... px?id=2913
Smartside Panels are a major improvement over the old hardboard siding law suit stuff. Smartside is actually a result of the law suits and siding failures from Louisiana Pacific, Georgia Pacific, Masonite, Abtco, etc. Smartside is a Louisiana Pacific product.