Questions On Ply Tanks

I am planning on building a plywood tank 3/4" 36x36x24" with 2 viewports, i
was wondering if i should make a cut out support frame for the top 2", or if
thats nicisary, i've been doing alot of reading and reasearch, but one
question is, after doing a few coats of a 2 part epoxy paint everything's
done let harden etc... how fragile are the walls to the edges of live rock?
just wondering if a stack of lr could make an indentation through the epoxy
crating a soft spot?


Thanks