Do a rubbing of the base to make a pattern of the outline and hole locations. Using that pattern cut a ¼” aluminum plate with appropriate holes for carriage bolts. Leave “ears” at 3-5 places to accept anchor bolts.
Carriage bolts may be inserted in the round holes and slid into the adjacent channel. Hold in place with scissor cut aluminum flashing.
After attaching the plate with nuts and bolts, a bead of black silicone sealer may be applied around the top edge of the plate.