I'm the original poster.
Problem solved. Turned out it was the battery. Thank Google and a local mechanic that I found via Google. Owner drove to me, turned key, expressed opinion it is the battery, gave me a jump. Total time elapsed 90 seconds.
He said leave it running, we punched his shop address into my GPS, I drove to the shop, auto parts truck showed up 5 minutes later.
No need for any tow.
Two lessons learned.
This was my own fault. It was original battery in 2016 truck, over 6 years old. I thought about replacing it as preventative maintenance but it was working fine. I thought a battery would give warning before failure. As above discussion said, I now know not necessary.
Now Google the topic I was living on borrowed time. Battery should be replaced after 4 to 5 years. Especially if going on a road trip I going to replace after 4 years after this.
Second lesson is if possible forget Good Sam or AAA towing. That's for when you are really stuck. If possible call a local mechanic. Same thing happened to me in a remote area of Florida. Truck was still under warranty and had towing. Talked to nearest dealer 150 miles away. It would be covered by warranty but started becoming very complicated including a 150 mile tow. Meanwhile someone who worked at the campground said call Larry the local mechanic. He drove out and had it fixed in 5 minutes.
I did consider giving it a try to buy a battery at Walmart. Since I was stuck in the Walmart parking lot for 2 nights waiting for Monday morning I wandered into the Walmart auto section. Found the batteries but the book to look up battery types didn't include my truck. Gave up. Besides at that point was before I posted here and learned batteries do die suddenly. I was convinced it was something worse and that replacing the battery probably wouldn't fix it anyway.
About the camper batteries powering the truck. The camper dealer once told me that the batteries are just wired together. Specifically he said when plugged into shore power the engine battery is being charged. That's all I know. There is a battery disconnect to prevent the camper from running down the engine battery but I thought not in the other direction. But above posts say with the distance and wire gauge the camper batteries won't be able to turn the engine. Interesting idea whether you could physically move a camper battery to the engine compartment to jump the truck.
Now here is a real laugh. From hints above I just googled and the Walmart I was stuck at has an Auto Care Center that was even open on Sunday. I could have asked a mechanic there. Oh well, I made it to my destination campground in West Yellowstone only 1 day late so all good.
