Thanks to both of you for your responses. 24 hours later, I have a story to tell.
I called Good Sam Roadside Assistance, as stated in my first post and will have a problem dealing with them in the future due to their inability to help me out in a time of need. I guess 24/7 service really doesn't mean much.
After I called them, I called my mechanic in Florida on his personal cell phone number because he told me long ago to call him when I'm on the road if I ever have a problem and he would try to help me via phone however he could. When I explained to him what had happened and the fact that the coach was still drivable, he knew exactly what was wrong and what to do.
He told me that the Workhorse chassis with the Auto Park, either by option on the smaller units or standard on the W-24, have had a problem with the design of their valve from the fluid resevoir. It apparently has a bad habit of wearing out after a few years of use and allows the fluid to leak out. The fluid is what keeps the parking brake from clamping down on the drive shaft, so when it is depleted, the brake sets and if you are driving down the highway, it will super heat the drive shaft and drum of the brake, ruining both and causing an extremely expensive repair. When I told him the coach would still roll forward when in drive, he knew the brake had not yet set and that no damage had been done yet and told me to check the fluid level. If it was low or empty, add ATF Dexron III to the tank and then keep an eye on it until I get back home. That was the case. When I checked the level, it was completely depleted, telling me that I must have stopped the coach in time to avoid damage. I filled it with ATF and the lights and beeper went off. When I put the transmission in park, the brake still works, so all is well other than having to have a new valve installed. My mechanic told me that he has been using a different, more expensive valve to replace the originals that will never go out again and doesn't understand why the manufacturers don't put out a bulletin explaining the same.
I hope this may help someone else in the future. Apparently, it is a fairly common malady on Workhorse chassis.