The Mantra gullwings are a nice boat, I believe constructed in Tenessee and Kentucky. The bottom is the basic same boat as an Earle Smith (Performance Jet Boat) 18' straight side gullwing, which is the same as a Sunkisst, CP and Scott Seastrum gullwing, etc. Originally a derivative of the Youngblood TX-19, Earle narrowed and made the side vertical and shortened the length in the neighborhood of a foot.
You can do a search for "wingers" or go to the club section of this forum and look for the WFL crew, (wingers for life) and you should be able to get a lot of information and pictures. Hotbo on that forum is assembling a new Scott Seastrum version now.