I have converted many float planes and yes the glass is more durable but most of mine are monocoat over balsa sheeting either built up or foam. They do just fine if time is limited on the water which all of mine are and care is practiced in beaching (thats another interesting skill to be learned).

But definately as I posted earlier check the floats If they are built up types (appear to be Goldberg) shake them, its as simple as that, sufficient water to effect inflight trim changes will be obvious.

Now let me address another issue that applies only to some of the NitroPlanes ARF's called Super Seniors.

I do not not what version of the Senior yours is but most of the Nitroplanes Arf's have been coming through with a very substandard fuselage pushrod set. It is a strange punkwood dowel perhaps a little less than a quarter of an inch. All most all seem to have a curious spiral corkscrew warps in them and if you actually use them The result will be wet noodle pushrods. Now on the elevator the blowback can be quite severe resulting in exactly the symtoms you speak of.

There are now something over twenty of the Super Seniors flying at our club and the solution has been abandoning the stock rods and replacing with Carbon Fibre rods from the pylon suppliers the type that stock 2.56 rod ends are a slip fit.

The test to check for a wet noodle pushrod (especially elevator) is to turn the radio off and by grasping the control horn of the elevator able to push the servo in both directions without noodlin out (bending and unable to move the servo when pushed).

Just a thought.

John