That looks like a good system for traveling long distance. Only problem for me would be that I don't always want to take my cat along when yaking is all I want to do. I also made a sailtube similar to yours(thebeachcats.com is a great place to "borrow" ideas from). The pictures I remember seing at the time had some sort of rack bolted to the trailer, wish I had saved the pictures now
Maybe it's possible to mount some sort of cradle to it and strap the yaks to the tube. I ended up making the doors for my sailtube twice because the stainless steel straps had distorted the shape of the tube...ah well part of the learning curve I suppose
Thanks for posting the link btw