Take a look at any recent Pete or KW with a flat top sleeper and a fairing on the roof. They have an extra panel to enclose the fairing now to keep people from sneaking up there for a ride. Big problem at the border.
A few years ago I was talking to a driver in Eagle Pass. He had a flat top with a fairing. He told me the last time he was in Eagle Pass he stopped at the Pilot to take a leak on the way out of town. He got to the check station on Highway 57 and they asked the usual questions, Are you a U.S. citizen? Anyone else with you in the truck? He said yes to citizenship, no to passengers.
The guy told him to pull into inspection bay 2. He didn't know what to think as he pulled over into the bay. Suddenly there were six or seven border patrol officers surrounding his truck. Turns out there were two guys hitching a ride up in the fairing. Border patrol told him a coyote must have sneaked them on while he was in the Pilot. They let him continue on, minus his passengers.