Getting ready to go with some 37x12.5x17s on my F250, and have largely decided on carrying two spares in the bed. To paraphrase, most folks who carry two say "one spare allows you to get home; two spares allows you to keep going." Over the next year, my wife and I are slowly downsizing to full-time living in an Airstream travel trailer. Our intent is to spend most weekends exploring the Western half of the country, with at least a few longer trips a year. I want these trips to go as smoothly as possible, so among many preparations, being able to swap one spare and keep going without a worry is nice. Worst case, I have personally experienced two flat tires on a bicycle miles off the road, and have seen it happen with two tires on the same side of a vehicle. So, again, it is a little extra piece of mind. I do carry and know how to use a plug kit for simple tread holes. However, I am not quite confident in my ability to reliably remove, remount, and reseat a tire. So, I am not really considering any major tire repair or even inner-tube installs as realistic options right now. My basic plan is to build or buy a cross-bed rack and mount them flat on top (roughly even with the roofline) to leave me more practical horizontal bed space. However, I am considering mounting them vertically. How have you guys carried two spares?