We designed the panel to be spot welded in place.
I think punching holes and plug welding could be tricky.
We have a 3-Phase unit with extended arms and we normally begin by completely cutting out the roof
We then hold it into postion by support from below using plastic water pipe and then spot weld starting in the centre and working outwards
We fill the edge with a metal loaded filler such as U-Pol D
Before priming and painting
I am sorry these photographs are small - I messed up the file in Photoshop.
Next time we fit a panel - within 3-4 weeks - I will produce some better pictures and produce a more detailed set of instructions with larger photos.