Most of the drivers had to wait about 8-9 hours for the mud to gel so they could walk out. Watching it on the news, the helicopter flying overhead the truck camper looked to have a full floating rear axle so it may have been a 3/4 ton truck.
Semi trucks with dry vans that were empty were picked up and washed to the side. I load trucks and often run the papers so we're talking about 30,000 pound, or more, vehicles just washed away. Flatbeds that were loaded stayed in place but the mud is up to the trailer decks. These are about 5 feet off the ground.
I was a rescue volunteer for 10 years. I can imagine on the truck camper, the lower part of the truck isn't the only thing brown there.