Good Evening,
I’ve have no experience with coolers like the one you mention for water storage. But there are some options in the 1 gallon range. This site has some wonderful information on water storage. Simply put “water brick” in the search box on the upper right of the screen for information on 1 gallon stackable containers. You are wise to recognize the question of lifting ability in storing water. As with all things preparedness, space, money, and your energy level are all considerations. If you are not already aware of them, let me offer a couple of possibilities in the 1 gallon and under range. Blue Can water sells water in 12 ounce (I think) soft drink size cans that is good for YEARS without doing any rotating, and the cans will fit in lots of small storage places in your house and car. But cost is a factor. I’ve also had good luck with Puravai water, which sells water in 1 liter bottles and is also good for YEARS of shelf life. But again, cost is a factor. But if you factor in that these two sources come in their own containers, there is no need to buy your own containers, no need to buy bleach, etc. to clean containers regularly, and no need to carry around lots of water weight to maintain rotation, these two might be a good option for you. And there are folks on this forum with WAY MORE experience in these matters than I have. These are just the two sources I use. There are LOTS of options for water, containers, filters, reverse osmosis, etc. on the market. For our household, I use the two sources mentioned above for long term storage drinking water storage, and use rotated (reverse osmosis) water for cooking, cleaning, hand washing, etc. Our “rotated” water supplies are in 10 liter and 20 liter Scepter water jugs, also shown elsewhere on this site. But a 20 liter jug full of water is roughly 45 pounds.
Let me encourage you also to consider the structural capabilities of your water storage area in making your plans for water storage. There are 55 gallon drums out there made specifically for water storage, which can be both filled and drained by hand pumps a bit at a time so you have no water lifting to do as you use the water. But if I remember correctly, water is 7 to 8 pounds per gallon. Not all homes have floors that are built to take 400 pounds dropped on them in a couple of square feet of floor space. Good Hunting!