You might wanna rethink that through Jim !!
"Not air tight"... try being pressurized so the passengers can breath and not pass out at 35,000 feet.
As for floats having to be sloshed to be water tight..... in my books that's right up there with the guys that coat their old leaking tinny with fiberglass or box liner crap! Do it right the first time... or go home.
I have 4 amphibs in the hangar right now... there will be 5 come Wednesday. Not one of them leaks a drop (and they can sit in the water for 5 months at a time) and there ain't no slosh in any of them, I can guarantee that as I built all 5 sets of floats!
...oh and as Bunk and DanC can tell ya.. mine have landed is some ROUGH waters! Not that I wanna try that little Lake Nipigon in 4 footers ever again...but I did and survived to fish another day. (on float skins that are less than 1/2 the thickness of any aluminum boat an OFC'r owns!).. I also land and take off faster than any Aluminum boat here.. including mine.
Welding vs riveting is an argument that will live on and on and on here. Ask a supercub owner to look in the logs and see how many times in the aircrafts life that they've pulled the welded fuel tanks out to be fixed... because they crack beside the welds from wing flexing. My riveted wing tanks have not, nor do I expect them to ever, leak a drop. I know.. I just jinked myself...
As for Wayne getting a crap boat... like many others before him. I've had more than one Tracker in my shop for patches. Can't imagine the total number of them out there...