Honestly I have built and used a few floats. I didn't have any luck with them personally. I can't say I really gave them a fair shake though. When I used them it was late in the season when the easy rats were gone and icing was and issue. It was also on a stretch of river where the current, and up and down water was constant problem. I don't have any pictures of the floats I built and they are long gone so I can't take pic's. They did ride nice in the river and may have actually done well earlier in the season. I just find it easier to blind set rats on the bank slides or in bank holes.
The floats I used were dry logs about 3-4 inch diameter cut on one end to form a V with the legs 18-20 inches. I then spaced lathes across the bottom to make a trap bed. they were anchored in the river pointed end up stream. I had 2- 1 1/2 coils on each float but a person could surely use #1 or 1 1/2 long springs as a catch would fall off and drown. I just used the coils because I thought they fit better on the float. I did have beavers try to climb on the floats, evident by the hair in fired traps.
Mac