any RO unit will have 3 small 1/4" pipes. One is the water in, one is the RO water out and one is the waste water out.
You can put the unit itself anywhere. Under a bathroom sink is a great spot. You can tap your supply line off your sink water, and put the waste water to the drain. If you go to home depot and ask them for adapters to connect 1/4" tubing to the cold water and P-trap of a sink they can help you out there.
For the RO water, well run it where ever you put your bucket/tank/trash can that you want to use to store the water. If you plan to use it a lot, I would get a REALLY long line and run it in the walls or ceilings. If you only use it once a month, then just coil it up and store it under the sink until you need it.
If thats to complex for you, just get a trash can, mount the RO to it and get a garden hose adapter for the RO. I had mine like that for years before I got a house with a basement.