This mod will create a new reward after completing certain sets of missions. It will add parked Gang Vehicles on all three Police Stations, which will always be unlocked, and will be yours (Cops won't chase you if you enter them). There will be two gang cars in Portland, 3 in Staunton Island and 2 in Shoreside Vale.
This is a screenshot created by me which gives you a basic look how the mod looks like.