I too would like to know, they are built on truck chassis and rated as 1/2, 3/4 and one ton trucks.
Heavier step vans are allowed.

The El Camino is just a car with a bed though, so I get that.
Don

1967 GMC 9500 Fire Ladder Truck
"The Flag Pole"
In the Stovebolt Gallery
1946 2-Ton grain truck
1946 3/4-ton pickup,
1953 1-ton pickup
1957 1-ton flatbed dually,
1954 Pontiac Straight Eight
Of all the things I've lost in my life, I miss my mind the most!