Thanks for the info. I don't have a dog yet.
The dog(s) I am considering are going to be very big, in the 150 lb area. I wouldn't put them in the bed without a bed cap or "topper" as some people call them. That is why I am looking to get one. To keep them safely in the bed with no chance of them getting out, especially when driving. I am not talking about a tonneau cover, which I already have. If you are not familiar with a bed cap it is bolted on securely and basically makes a pick up bed into an suv or van like area.
On the other hand having a 150+ lb projectile in the back seat could possibly kill the passengers in the front seats in an accident. So a dog or two securely kept in a bed with a cap on it is the safest place for them to be. Safest for themselves and the people in the vehicle too.