Depends. Back in the earlier years, Bob W., suggested using two pressure treated 2x4s, laying on gutter clamped roof racks to mount solar panels.
Of course, that wood is NOT mounted directly ON the roof, it is u-bolted to the cross tubes. The bolts to the panel Z mounts are through the wood, with washers and nuts as necessary.
I used that method on a E-350 to mount 4x100 Watt panels, with no issues over five years of varied weather, with a reconfiguration at one point, to gain room at the rear to secure a short step ladder.
Of course, that wood is NOT mounted directly ON the roof, it is u-bolted to the cross tubes. The bolts to the panel Z mounts are through the wood, with washers and nuts as necessary.
I used that method on a E-350 to mount 4x100 Watt panels, with no issues over five years of varied weather, with a reconfiguration at one point, to gain room at the rear to secure a short step ladder.