I'm sure you remember that my family had a 1971 Ford F-250 Custom pickup. Well, in 1971 Ford recommended that customers who buy F-250 Camper Specials haul campers that were 11 feet long.
http://oldcarbrochures.com/main.php?g2_itemId=82996
http://oldcarbrochures.com/main.php?g2_itemId=82999


My dad's truck wasn't even a Camper Special, and it hauled a 12 foot camper!