Spending $35 (for two) just to keep your P2V from sinking, but guarantee
that it is submerged... seems like a sub-optimal choice.
With inexpensive foam pontoons, at least there is the chance that the
P2V would stay upright, at least in calm water with not much wind.
To be more effective against tipping over, the floats need to stick out
roughly past the tips of the blades, perhaps as a cross located to avoid
prop downwash, as much as is possible. A diamond-shaped cross section
might help the downward air flow past the pontoons, and perhaps help with
a cleaner, less "sticky" takeoff. A large quarter-round on the outer ends of the
pontoons might help to keep them from "digging in" as it landed.
Easier to attach might be a cross oriented under the P2V's arms.
Coating all the electronics (but maybe not the heat sinks) with a
waterproof, non-conductive conformal coating might be a good idea,
keeping it thin to reduce excess weight. Somewhere in this forum,
I believe, somebody was "advertising" their special super-thin
waterproof coating, but it was a bit expensive for them to apply
it properly, around $300 as I recall.