About to drill through the roof to mount solar panels- tips?

I used the Unisolar 68-watt ones for my TT and they were OK but if I had to put additional panels on my TC I wouldn't get them again. They are really big for the amount of power they produce, and are difficult to handle when you are trying to stick them on. Because they are so big, they were usually partially shaded and that really affects the power output. They have also gotten a lot more expensive in the past 2 years for some reason.