Mark out on roof. Predrill holes. Lift solar panel a bit and use caulking (whichever you think is best) under the mounting bracket (this is to stop rain getting under the bracket and making its way to the screw hold and allowing the start of rust). Press down. Start putting screw in. Just before it is totally in add some more caulking to squeeze around the screw for the last part of the tightening. This should ensure no water makes its way to the hole under the bracket and under the screw.
Rails would preclude the need for z brackets, and you could minimize the number of holes drilled into your roof. 2-4/rail vs 4 per panel. Also, using z brackets atop a rail would give you extra clearance space for heat
Mark out on roof. Predrill holes. Lift solar panel a bit and use caulking (whichever you think is best) under the mounting bracket (this is to stop rain getting under the bracket and making its way to the screw hold and allowing the start of rust). Press down. Start putting screw in. Just before it is totally in add some more caulking to squeeze around the screw for the last part of the tightening. This should ensure no water makes its way to the hole under the bracket and under the screw.
I like the idea of caulking silicone around the hole as you screw the bracket down.
Finally a video I really wanted
What about mounting to a house roof. Do I need rails, or can I just use the Z brackets?
What type of roofing material may help answer
Rails would preclude the need for z brackets, and you could minimize the number of holes drilled into your roof. 2-4/rail vs 4 per panel. Also, using z brackets atop a rail would give you extra clearance space for heat
What would you recommend for bigger panels on a metal roof? 300-400 watt panels?