Originally I had trouble getting the hatch to seal, both at the top and at the bottom. I eventually fixed that by using two seals at the top, and wrapping the lower seal onto the floor.
I think the question you are really asking though, is, "Does the wooden web inboard of the seal add any sealing capacity?".
I guess, if you didn't have a good seal, it would add a layer of protection. But that extra layer of wood sure weighs a lot.
I guess it depends on what you feel comfortable with, both initially, and 10 years from now. Would I buy on of Steve's teardrops again? Yes, Absolutely! But I would also use the same weatherstripping that I used on the Generic ET.

The quality is remembered long after the price is forgotten, so build your teardrop with the best materials...