Well, since it sounds like you have another car anyway, as long as you carry collision on it you should be okay I'd think ...

You know, another potential problem with a mini-lease would be what happens when you are renting two cars at the same time (i.e., you have one on mini-lease and it's parked at the airport while you fly somewhere else where you also rent a car). It seems to me that you could have problems if something were to happen to the car at the airport while you were away and the insurance company found out they were insuring three cars at the same time (this could especially come to light if you had really bad luck and something happened to both rental cars during the same trip ...).