GFS,
In my opinion there are too many hard PVC spray rails already available, like the ones I bought at Hamilton Marine (But never installed), to make it worth the effort.
http://store.hamiltonmarine.com/brow...------160440/4,12529.html
With that said, I think there may be a market for a well designed soft one. If you went with the softer one, then using the high tech adhesives is the way to go. The softer ones are much lighter, much easier to ship and you can probably design a shipping system that does not require special trucking. On top of that they are easier to mold to the hull. If you went with the harder type, then bolting through would be my choice with lots of 5200 to prevent leaks. I think there are applications where both are needed. Cape Island Boats only uses the Hamilton Marine rails, and bolts them on (They finish Duffy's). They say Hamilton is cheaper than going to the manufacturer in Mass because Hamilton buys in such volume. In my opinion I would like to see a rugged, soft, durable and light design that I can glue on and paint to match if needed. I have nothing against the Smart-Rail except they are way over priced, but they can argue there is nothing else like it and they are correct. If you did make one similar to the Smart Rail, but different enough to avoid a lawsuit, I can assure you the Smart Rail price would plummet, so that is another thing to consider.
Good Luck,
Dan