Here are a couple of pics on our Pet 'Bed' in our F350. It sits on the rear seats after folding down the seat backs, then is supported by 3x 2x4 legs along the front, right behind the front seats. Make sure you locate your front seats before measuring for the deck board.
In the 4th pic, it shows a hinged addition (cover removed) that folds down on the center console at the height of the bed. It's there to fill in the gap between the console and the bed (since it sits about 4" higher) to make sure they don't step in the hole when entering or exiting, and serves as a nice perch for the one laying down the center. Our Chow/Sharpei/Rottweiler is the best rider (as long as she can navigate, you can drive), and lays right up the center onto this console. The others lay on either side and look out the rear or side windows.
You can tether shoulder harnesses to the rear wall on the 'child seat hooks' that you can see on the back wall.
The side view picture shows the 2" foam mat and the washable blanket we use to cover it all.
The longest trip we made was about 4 years ago, when we made a 4 day round trip from Illinois to the LA area (~1000 mi/day with 2 drivers), and back with our flatbed, to pick up an antique truck. Two dogs (at that time) made the trip with us using this bed, and loved every bit of it. Had to say in hotels on that trip though.
And don't forget to take your dogs' records with you.
4 R PETS !