I think it would be perfect for waterton (yeah, waterton wagon is a great name for it
I used a backpack system to portage there and my shoulders still hurt afterwards- had to stop several times to rest. (I'm smaller than most of you guys who run waterton!!
) A cart would be awesome!
I have one for my canoe, but it's definitely too big to use for my kayak. You should post pictures of the finished product when you have it! I may have to buy one if you put them in production
check out the wildwasser canoe cart, it may give you some ideas on design. it uses straps to attach the boat to the cart. works great!