A good set of roofing sheers will usually handle tank wall material.
A thin disc makes a lot of sparks if the tank walls are thicker .
Think Plastic , 2 tanks if one is hard to fit.
I have worked with these folks , a minor sketch or a visit will get the fill.drains in just the right spot.
There catalog is marked with which can travel UPS , a great cheap way to ship.
Fresh or Black water they make both.
DURACAST | ROTOMOLDING PLASTICS FOR THE FUTURE
duracast.com/