For many years, I avoided mounting the solar panel on the roof of my truck. Here’s why:

• Many places I camp are shaded, so the panel will not put out much current.
• At a flat angle the panel is less efficient then angled towards the sun
• I didn’t want to drill holes in the roof of my truck cap
• I didn’t have a good way to get power from the truck cap roof to the inside of the cab of my truck.

If “fixed” those problems by:

• Re-thinking how I’m using the panel. I no longer look at it as for it’s peak efficiency but for the fact that it will be on my truck wherever I go, and mid-day parked in a lot somewhere while I’m hiking or kayaking, it will be charging. Maybe i won’t get a lot of charge while at camp, but if my battery is back up to 100% by the time I go back to camp — even after just a short drive — I will have ample power for night.
• Solar is “slow” power, it’s charges things over time. Even I am not peak efficiency, if I’m parked in a bright and sunny parking lot it will recharge battery by the time I’m back at the truck. My relatively small deep cycle battery (100 Ah) with my limited power consumption (generally under 2 amp 12 VDC) works well with the fairly large 100 watt panel.
• I built a cross bar rack and got the pins that allow me to bolt the panel to the Yakima rack. It’s removable for maintenance and didn’t involve any drilling into the cap, potentially creating leaks.
• I found a grommet in the floor boards of the truck that was made of plastic that was easy enough to drill through.