Havis:
Macojoe may be referring to foam, but Wellcraft has been advertising the flotation properties of the Steplift's double-hull design since at least 1970. Check out the old brochures on this site, including this one from 1971:
http://www.wellcraftv20.com/gallery/...amp;id=page004
Your question made me look at some digital copies of brochures and ads I've collected. One Wellcraft ad from 1970 actually touts the advantages of the Steplift's "built-in air flotation" design over others that use foam. I thought I had copied that ad from this site, but I don't see it here. I'll have to send a copy to Tim.
Fitz