We negotiated the spare and the spare tire carrier as part of the deal before we closed.
This is the carrier that we got: Roadmaster Inc. - Tow Bars, Braking Systems & RV Accessories
Not cheap, but that's why I got the dealer to pay for it.
We're in the "never travel without it" group as far as the spare is concerned. Relying on roadside assistance to find the right spare for your unit is very "iffy", and many have ended up with an off-brand tire at an inflated price. Much better to have your own spare, and let them change it.
We got the Ford platform (26XD), because it has the 6 speed transmission, and is quieter than the Chevy platform, and gets better mileage (almost 12 MPG on the last trip). The cruise control is great! We we're able to use it most of the way through the mountains, and with the 6 speed, it held speed perfectly even on steep downhill runs.