When I bought my F350 I got the trailer TPMS monitoring system. So far, I have been very happy with it. Unfortunately, the Ford TPMS cannot monitor the spares. The nice thing about the Ford TPMS is there is no sensor to have to fool with when I manually check tire pressures and I don't have another device cluttering my cab.
My practice with spare tires is to keep them inflated to the maximum allowed for the tire and then lower the pressure to the correct pressure when I use the spare. I also carry an inflator so in the worst case I can add air to the spare.
I think I will add checking the spare tire pressure to my travel checklist, although it is a hassle to check the pressure on the Oliver spare. When I got my new truck, I lowered the spare and flipped it around (Ford has the spare with the valve up from the factory) so that I could check the pressure with it mounted under the bed.