Tow Vehicle w/ Best Back Seat for Passengers - Ram Mega Cab?

I believe the OP's intention is to tow a 9000lb travel trailer with a cab full of passengers. That does not require 2-1/2 tons of payload capacity or an 8ft bed.

Folks have been getting along fine with 6-1/2ft beds for decades now. I personally have not found anything that made me stop and say, "Gosh golly gee, I wish I had an 8ft bed." I've even hauled 16ft lumber in a 6-1/2ft bed. I'm not traveling from West Virginia to Colorado like that, but I sure can get home from Lowes.