74, You might want to check out the floats made by Falcon. They are light, and pretty rugged. I have a set of 33 inch (only size offered) on my Kangke SK-50 with an OS 60 FP up front. Plane weighs a little over 8 lbs dry. Was able to use the stock landing gear and put a second one behind it mounted to a plate. Floats are made of ABS plastic, joined with very good seams. Haven't had any leaks in about 20 flights. The floats are ready to go, and come with the mounting hardware and a water rudder. I painted mine with Krylon Fusion silver and finished with a coat of clear Lustrecoat.

I have been considering both the Seamaster and Mariner also, and after flying both and observing others flying them, I will probably go with the Seamaster. If you read thru some of the posts on these you will discover that the Mariner flies well, but is plagued with the covering coming off the bottom of the hull, and an engine pylon which does not hold up and is difficult to repair.

Best Wishes