I used to work at a lumber yard. On occasion, a customer would load his truck in the same manner, or request that I do so. I discouraged the former, and refused the latter. The likelihood of cracked windscreens was too high to risk it. We were fortunate that our manager supported us, as it concerned this one particular and apparent refusal to assist the customer as he requested.
I've had a few 12' piece of baseboard in my JL (an actual JL, not a JLU) and drove about 10 miles @ 65 MPH. Stuck it through the passenger side window and rested between the passenger door mirror & door frame. FWIW: the JL is only 13'-11" long, and the front of the baseboard was about level with the grill.