I installed mine over bare concrete to allow any large spills of water to run out of the garage just as they would with out the tiles.
The tiles have an air space to allow for the passage of air or liquid under them. They do have a hollow sound to them when walking
with hard sole shoes but once they have cars, bikes and other objects on them it is much less noticeable. You can use landscaping fabric under them to reduce the sound but that will absorb spilled fluids and reduce to ability to have drainage under them.
In my experience very little if any thing spilled on these actually goes under the tiles as the joints are very small but vary a bit due to changes in temp. When I got mine they had a garage journal member discount with free shipping and they came via UPS a few days later and my 6 yo daughter and I did the install in a few hours. The Race deck web site has tons of great photos and a design tool.