I’ve had the 8gal weekender (bought via Costco online when on sale) on the roof rack, perpendicular to the direction of travel. This puts the pump handle (purchased separately) and the hose connect right over my rear passenger door, and the pop-out shower tent we have. It’s been amazing to have a nice warmish shower on long trips, and the hose is long enough to reach the tailgate for washing up. yes, you have to pump it a lot, especially when the water level is low, but it’s worked well from day one and I have zero complaints.