A boat sandwiched between two trucks. As seen on the TV show "Squidbillies", driven by Early Cuyler.
"Wouldn't them fine-ass speakers sound gooder than hell comin' out the back of my truck-boat-truck
A Truck-Boat-Truck is what Early drives on "Squidbillies". It's a truck, hauling a boat, hauling a truck.
"Lord please forgive me for stealin these sum-bitchen speakers that would sound gooder than hell in the back of my truck-boat-truck"