On the MBR2 seaplane there are hooks on the hull and wing floats which control the flotation level in the water
Ok I can only do as far as the FM and class files. I've asked beo and this is what needs to be done in the 3D and hier.him:
The floats need float hooks, the float meshes replace the gear meshes both in the plane folder and hier.him (Some of this could be copied from Ar-196A3) The way the floats are placed will affect how it floats, and whether you can actually take off or land. Take one of beo's new float planes from the aircraft section and look at the hier.him file and you should know what he means by how the plane will float.
The rest is class file and fm stuff. Tell me when you've done the above^^.