I have been wondering, would it be possible to make an 8’x4’x’5 tank that can be put up and taken down as needed, where you would have a base, four removable corner posts, more removable posts as needed to support the walls, and a top connector. Use either water pressure or expanders to hold the walls against the seals, and only one wall would need to be clear. For even more extreme have the base be in multiple sections so it can fit in the back of a car.
I ask because many of my friends and myself are mermaids/mermen and we don't always have the funds to buy a massive 1000 gallon tank and the trailer to move it. The tanks allow us to set up and entertain kids in dry environments, like a building or a fair. I know water has the pressure to keep a car door from opening when a car goes into a lake, and I would imagine having water push against a wall will make a fairly good seal, and the bottom could be lip connector based. I don't think it has to be 100% leak tight as it might only be set up for a few hours and something like a tarp could be placed under the tank to collect the water and pump it back into the tank.
How insane is this idea?