Hey Dennis,
I have considered doing the race only haven't figured out the part of taking off 30 days off work. The only person to complete the race on a cat is crazy russian.
To his credit he completed in a very respectable time using an inflatable cat with a full size collapsible mountain bike and trailer.
Having completed the NCC Challenge twice and what I learned last Sept I will be happy to relate to you.
DO THE MATH!!! An inflatable boat or an A-cat can weight in under 450 pounds. An Isotope with two people and gear can hit the scales at 800pounds.
Think about it rowing against the flow of the river 100 miles.
The folding catamaran is ingenius but either needs a longer waterline or super bouyant hulls.
My best idea is an A-cat with a 3/4 high mast, bmx bike, and a frame to turn the hulls into a trailer. This sound like a fragile way to go but it keeps the weight off.
The inflatable catamaran is still a very good candidate. The things I would do different that Crazy Russian would be longer oars and maybe a double centerboard setup but these items take weight.

Good Luck,
J.P.Ayers
Isotope 186
Holdyourcourse