I don't see why the panel screwed into blocks wouldn't work for a wider area - it just might need two rows of fasteners.
As for the adhesive
used for the blocks...
In my Boler
the central ceiling-mounted light
fixture was mounted to a similar plywood block. It was likely originally held with fiberglass resin, which may not have cured properly, and apparently fell down, leaving the block, fixture, and area of foam lining supported only by the lining and wires. A previous owner cut slits each side of the block and injected some adhesive, which was likely contruction panel glue. Somehow, they missed getting it behind the block and just gooped it all around, and someone followed that with silicone sealant, so I had to cut out the whole mess and start again.
In the end, I glued in a replacement plywood block with construction adhesive, and it has held just fine for the year it has been in place. As I recall, I used LePage Bulldog Grip PL 700 Tub & Shower Kit Adhesive
, because it is a high-strength product designed to join plastics (such as fiberglass panels) to wood.