Contrary to popular opinion, I've found that moving the floats on a flat bottom trainer forward an inch or more (in front of the CG) improves their take off performance dramaticaly. Particularly if the nose of the floats is a little short to start with.

I attribute this to the effect of the strong downthrust built into these airplanes trying to bury the nose of the floats before flying speed is reached.

Try it as-is if you'd like, but if you notice a tendancy for the front of the floats to dig in, move them forward and try again.

Jim