Take a look at my build thread to see the underside access: (Single post here:
So the build begins... ) Thread post
http://986forum.com/forums/general-discussions/35002-so-build-begins.html
I was able to access everything without problem. As for storage, the unit has a lifting pin to roll out of the way if you want, however, we simply park either car over the top of it. The Boxster can do it without using board risers (on good suspension). Robins car simply drives right over the top without issue.
Note: if you do have to lift the car to get on it (as mine started out with a shot suspension) I only needed a 2x6 to get up on it.