Hi HDs,
I know this is a somewhat late reply but did you ever get an answer on this one? We usually fly with Emirates whose standard luggage allowance is 30kg each. We usually take a case each, last time mine weighed 26kg plus hand luggage of 5kg, Tony's was 23kg plus hand luggage of 5kg, plus the dive kit which was packed seperately and weighed 15kg - and had no problem at all with excess luggage at the seaplane.
One thing we learned last time - they'll split the luggage if it's too heavy ie they'll send some bags on a later seaplane if the overall weight is more than they can take - it hadn't happened to us in previous years but last year we had to wait for our cases. No charge was made, it just meant we had to wait for our bags for a few hours to arrive on the next seaplane (apparently it tends to happen more if you're arriving on a Monday but I have no idea why that should be).
Hope this helps!
Jan