Hey David
Sounds like you're on the right track to me.
I don't see why you couldn't hook up any of the RO/DI units in the garage and just have it drain into some sort of closed container. I use a 5 gal bucket. You might want to look into some food grade containers that are bigger. One thing to be aware of with very pure water, keep it tightly closed because it will pull in contaminants from the air.
I use a large
submersible pump from Dolphin to pump our water around. I'm sure any
pressure rated pump would work for you too.
Spanks