Our panel did not come cheap and nor did the vans, brackets have twice been fitted behind roof light using bonding mastic. Mastic allows secure fitting with no holes into the roof. Behind roof light protects the panel from slipstream wind force and provides access for the cable via the roof light opening, white silicon mastic covers the cable neatly in the corner of the roof light and a slim line plastic trim on the ceiling hides the route to cupboard and the electrics.
When we changed the van everything was removed leaving the old van unmarked and undamaged and it should be the same if we decided to change again.
Removing the brackets mounting mastic was not easy, but better than having screw holes in the roof and cable access hole.
Closeness to the roof light also gives ease of access for cleaning.