After many months, I decided to move forward this model as well.
Given that my diorama is too small for the plane but still will to show it in the "water", I tried a different approach.
I purchased one of those aluminium pie backing tin of a suitable diameter (26 cm) and I filled it with several layers of resin.
The first thin layer was painted with acrylics in order to cover the pattern present on the bottom of the backing tin and to try to give a sense of deep.
Next layer, about 1 cm thick, was coloured with a few drops of blue and green while next two layers were transparent.
The result is this:
Of course I will have to remove the backing tin at the end, but it shouldn't be too difficult.
May be it's far from perfects I think I couldn't have done anything better.
But now I'm in a stage that I will appreciate any suggestion on how to go further.
My goal is to simulate this situation: a calm sea water with just little waves:
So, I will position the model with its floats on the top of the resin and pure more resin in order to partially submerge the floats.
That will work, but the new surface will be perfectly flat, how could I add some waves? I thought to use a brush to stir the resin when it's already almost solid, but it will be very difficult to do this under the belly of the plane, therefore, as I said above, I will appreciate any suggestion.
Many thanks
Alberto