I have reviewed it recently and my concern would be
1: water getting under the flooring [ anything with seems or sections ]
2: movement [ shifting ] from car movement.
Does Racedeck need floor prep?
I have Racedeck in my garage, it's been close to a year now, and I really like it. It looks good and the floor is warmer in the Winter than the cold concrete was. Plus, it is easier to walk on and easier to lay down on, although I seldom lay on the garage floor to work on the cars these days.
To answer your questions, water does not get under the tiles unless it sits there for awhile. I just clean up any spills right away and I have no problems with water under the tiles. But even if you do get water under the tiles, it will run toward a drain if the floor is sloped towards it, or toward the overhead door if the floor is sloped that way.
As to the tiles moving, that just doesn't happen, at least in my garage it doesn't. My garage is 24X36 so I have 864 tiles on the floor. The shipping weight was close to 900 pounds. With that much weight on the floor spread over a large area, the tiles just don't move at all, with one exception. I have a row of black tiles on the outside of the flooring, which it turns out is not a very smart idea on my part. This means I have a row of black tiles where the overhead door is and my overhead door faces east. When the door is open during the Summer months, the sun beats down on the black tiles and they expand a bit more than the other tiles causing the floor to buckle slightly right by the door. It isn't a real big deal, I normally leave the door closed on hot days and turn on the garage air conditioning. I just wanted to you to be aware of this so if you do decide to go with Racedeck flooring you don't make the same mistake I did and put a row of black tiles right by the overhead door where the sun can beat down on them.
As far as floor prep, yes there is some preparation, but it is VERY MINOR. All you need do is sweep the floor to get rid of the chunks, then vacuum the floor with a shop vac. That's it, the floor prep is now finished. Just lay out the floor to get started and once you get the initial few tiles started, it goes pretty darn quick. Since you have "bad knees" I would suggest you get some help putting them down, but that help can be anyone from the age of about 14 and up. Laying the tiles is simple and straight forward, anyone can put the tiles down, it doesn't take a rocket scientist to do the job. You will be done in a few hours at most and the floor will look great. In fact, you will wonder why you didn't do this a long time ago.