arl thanks for the reply, I'm rapped I can reduce the size of the plywood down to 1/16
I had a talk to a mate of a mate who has made some big tanks, he did a 14ftx2.5ftx2.5ft all glass for a customer of his.
Long story short I owned an aquarium store for 10yrs( no money in it
) my mate 30+ yrs and his mate 30+yrs. but they don't/can't help unfortunately.
He suggested building the angle iron frame fitting with plywood and lining it with fiberglass.
So now I will do some more research, I don't think I will bother with the steel angle iron frame as I am sure timber will be more than strong enough.
I will let you know which root I decide and I'll start a thread here once construction begins.
arl once again thanks heaps for your help.