I use a PaddleCart from http://www.paddlecart.com/. Its not perfect but its a good fit for a Kruger canoe. Especially if you are going to do any long distance portages.
I can tell you that mine did awesome pulled behind a bike for 40 miles during the UFC. I averaged speeds around 7 - 8 mph and topped out around 14 mph. No issues with tires or bearings. It also did just fine on the 1/4 mile portage at Big Shoals on the Suwanee River. One major feature of the Paddle Cart is that it breaks down into stowable parts. Very handy when your on an expedition style trip.
Things I would watch out for:
1. You will need tie down straps
2. The support bars are in line with the boat. I highly recommend add flat webing front and back to support the boat. On thinner hulls they have the ability to get crushed inside the cart if you don't.
3. The bearing carriers are not sealed. Lubricate them appropriatly. Don't let them get wet with saltwater and then dry out.
4. Don't overload the boat on the trailer with a 100+ lbs of gear or you risk bending the axles. I did it going down a curb. Any bigger bumps overloaded can be risky.
5. Put puncture liners inside the tires if you go anywhere with sand spurs or other hazards.
6. Carry spare tubes, tire repair kit and pump. Know how to use them before you go.
7. A 4 foot section of broom stick inserted into the frame makes a great kick stand. Its much easier to load a boat onto the cart solo when you use one.