Not a bad idea - properly installed tile is as tough as the substrate it is applied over. Two things to make sure of: 1) do a really good job of ensuring that the adhesive contacts the backs of all the tiles completely - no air pockets. If there are any air pockets, the weight of the car or dropped tools will crack the tiles easily. 2) use an epoxy grout like SpectraLOCK from Laticrete. This stuff is much more expensive and difficult to put on than standard grout, but it will not stain and is much tougher. I've used it in kitchens and bathrooms with great success. My wife and daughters have even spilled hair coloring on it and it just wipes off.