A portable shelter that attaches to the outsides of the tires of the vehicle, as opposed to the body or wheel hubs of the vehicle. The shelter includes a canopy attached to an upper end of at least one mast, and a mast base that is attached to a lower end of the mast. The mast base comprises a threaded bolt, a plate having a threaded opening for receiving the bolt therethrough, and a holder for receiving a lower end of the bolt. The base also includes a plurality of arms that each have a first end attached to the holder and a second end attached to a hook. Braces are mounted between the plate and the arms so that when the bolt moves relative to the plate, the arms move relative to the holder so that the hooks on the arms can receive the outsides of a tire.