The almost finished product. Tank coffin cover on and epoxy with cabosil layered to fill the void. We decided to lock it in as all sealants like silicone, 4200 etc all shrink with time and let water in. This will keep it all out and if we ever need to remove the hatch we can do it with a skill saw and a pry bar. You can always fix what you messed up on the first time. There is always a way.
I left the alternate fill pipe and vent for the second tank in tack so that if the primary leaks we can shift it to the secondary tank fill and vent.
A good day at the shop.
Captain Al Lorenzetti