I find it's much easier to have the RO/DI system in your house. This way you can control the water you put into your tank. I boought the Typhoon III from Airwaterice.com. It's a very good unit and I use it frequently. I have it mounted in my garage. I keep 3 brute 44 gallon garbage cans in my gargage next to the RO/DI unit. In 1 garbage can I keep pure RO/DI water, in the second can I keep salt water all mixed up and ready to go and at the same time I dose it for Alkalinity and calcium so that it matches what is in the tank. The third can keeps kalkwasser or limewater and I use it for top off. It works pretty well for me. I control what goes into the tank and it's all in an area that is easy to get to. In the winter it's really nice because I don't have to step outside. I would highly recommnd getting an RO/DI unit. It's nice to have all the water on hand that you need. It can be a disaster if you have an emergency at night and can't get water that is ready to go.
I hope this gives you some more insight.
Regards,
Pat