RE: Turning trainer into sea plane
The engine is enough, so it comes down to the floats. look for Chuck Cunningham's articles somewhere on these boards for how to size and build floats and/or look at my brother's simple way - no covering or anythng special and they work very well! - of doing it from pink foam from Home Depot and using the Cunningham princples.
You may also benefit from looking over the posts on the seaplane forum.