I have 2 Poly tanks outside for the same reasons.
They are each 1000 litres which I think is over 200 gallons. They are a different style, about 3-4 feet wide and 6-7 feet high. (Sorry not good on your measurements.)
I made a little wooden platform to sit them on and they sit in a small garden bed against a side fence. They are only connected to a tap, so thereis nothing connected that can use all the water without my knowledge (excluding the neighbours jumping the fence.)
They are a bit light when empty, so need straps to hold them down in strong winds, but with a little water they weigh down fine.
Ive had them sitting there for over 6 years and they work well.