The Seamaster was designed with flat bottom. Plans are still available from the RCM Plans service.
http://www.rcmplans.com/index.php?ma...oducts_id=1727

The flat bottom WILL let you slide it around on the water. It also makes it skip and bounce more easily on landing.

I rebuilt a flat-bottomed SeaCruiser after I strained it through a persimmon tree on the bank. I put in a shallow V bottom. I liked the V-bottom better.

I Don't know why you heard that landing the GP Sport Floats was "wicked Evil"...Even the most hated plastic blow molded floats will land OK.
Land like you do on the ground- glide in, flare, hold the airplane off the surface at a couple of inches high until you run out of airspeed and it settles in. Conventional full-stall landing. If you do it right, you can drag the water rudders for a while before you touch down. That is fun, too. Unless, at 3.14 pounds, the Sport Floats are just too heavy for your plane to fly at reasonable landing speeds.