I'm considering the same issue. I have a 180 litre tank and the novelty of moving water around quickly wears thin. I'm moving to a new 625 litre tank. The problems are increased 3.5x - so I need a solution.
Here in the UK, we don't have the "problems" of so much heat - mostly it just rains...
For me the ideal solution is to buy an outside shed and put the RODI and saltwater tanks in it. Then adding the RODI equipment and any electrics required.
The advantage of using a shed is: it can be atheistically pleasing. It can be insulated against heat/cold. It can be waterproof etc.
I'm also thinking of hooking up electricity, adding water in, water waste out and water to the tank. Drilling through and linking it through the outside wall is not so hard.
An alternative to a shed, might be a garden chest. We have one for some garden tools. They are about 150cm x 80cm x 80 cm. Not too expensive and very durable (made of a very stable plastic resin). They also have a realistic wood finish - to me, looks OK. There are other units that are taller and more suitable for storage. Water can be pumped between storage units - so no need to stack vertically etc. If necessary, I could buy and stack two chest...
One thought I had was not to mix too much water at a time. So exceptionally large tanks are not needed. Little and often might be best. For the tank, it is 625 litres, so a 10% water change is 60+ litres. After the first fill, not too big an issue e.g. storage for 2x 60+ litres.
BRS TV make water changes on a semi-industrial look easy when they have a fixed setup. One UK issue, is pipes can freeze in winter so outside pipes have to be lagged or heated. One solution is not to have outside pipes e.g. to add the pipework inside the house - either permanently installed or to be attached - on WC day. Adding water vs mixing it are different e.g. adding water takes only a few minutes to top up a reservoir. The time is in the mixing...
