Lesson learned: Don't neglect to check the spare tire

Just a reminder: check your spare.

I have a 2004 2619 and have been very much up on the maintenance of same, however I have never checked the spare tire because we always carry a power tire pump in the tow vehicle. I figured that even if the spare loses a couple of psi. per year we would always be able to top it off with the pump if we ever needed to put the spare on.
However we were getting ready for a trip to Hollister CA which is a very hot climate usually. While airing up the trailer tires I thought I'd take the time to top up the spare because I was thinking that I didn't want to have to do it on the side of the road in the 103+ degree heat we were heading into. When I got under the trailer and thumped the tire I was startled to find it completely and utterly flat, upon examination it was discovered that the rubber valve stem on the tire was swollen and severely split almost its entire length.
The tire store where I took it for repair said that since there was no way possible that anything could have come in contact with the valve stem where the spare is mounted, they thought it was a defective valve stem or was torn when the spare was originally installed.
Thankfully we dodged a potential roadside headache... so don't forget to check yours... often... I know we certainly will be much more vigilant in the future.