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.

While you are at it, you might want to dedicate some of your water supply to first aid/emergency uses such as flushing eyes, small fires, irrigation for burns, heat stroke, etc.

All those tanks seem excessively expensive. Even the big ones are around $1.00 a gallon and the small ones (15 gallon) are several $ per gallon. You can buy bottled water at the grocery store--FULL bottles-- for $1 a gallon or so. To store 30 gallons I'd just use bottled water or 7 gallon stackable jugs (about $12 each) if I wanted to be a little fancier. For cheap storage of larger quantities I'd think of PVC garbage cans (maybe 15 bucks at the hardware store for a 33 gallon can?) lined with polyethelene bags, or even a kiddie swimming pool ($100 for a 15 ft diameter, 3.5 foot deep one, about 3000 gallons) if you have the space for it.

I wish there was such a thing as cheap desalination devices and I'm not sure why they don't exist. I'm about a mile from the ocean which means I have infinite amounts of undrinkable salt water available. A Pur 35 lifeboat-type desalinator (hand pumped, 4.5 liter/hour) is about $800 on ebay and I play with the idea sometimes, but it's too much cash for me to spend on something like that, plus it needs maintenance (annual biocide treatment) even if not used. If I won the lottery I might consider a 12 volt unit (26 liters/hour, $2500) with the idea of powering it from a portable generator or a car.

They do exist. How cheaply could you make this?

http://www.permapak.net/solarstill.htm

However, getting the water from a mile away might be a more expensive problem to solve.

A

Those solar stills are cheap enough, but slow, not portable, and they need good weather (sunlight) and lots of space. Moving water from a mile away isn't that big a problem, even without a working vehicle, given time and muscle power. I could roll a 13 gallon wastebasket full of water on a hand cart pretty easily, or jam a few 1 gallon bottles into a rolling suitcase, or even just carry one or two gallons.

I've heard that most plastic garbage cans and most of the larger plastic bags that would fit inside one will leach "stuff" into water stored in it.

HOWEVER, I would not hesitate to collect rainwater in a [new] plastic garbage can in an emergency, and repot it into something safer.

Sue