Polaroids are layered components. I would not use any glues, heat, or pressure types of mounts.
You can use hinges, corner mounts, edge mounts, or a platform mount.
My preference would be the platform mount, totally noninvasive.
There was a photo there of the camera they used which was a huge beast of a thing made even bigger by its custom made underwater housing. I can only marvel at how they managed to get those shots given the complexities of the equipment and the fact that the (very game) model with posing with wild stingrays for some shots.
Corner pockets force the paper to stand on its bottom corners and provide little support otherwise. If this large paper has a tendency to sag, it would be a problem. And if a pocket comes loose and the art slips far enough to stick to the triangle of adhesive left on the mounting board, you're in trouble.
Why not the Platform mount? That would provide full length support on all edges.
I've had to deal with these a lot recently. I check with the artist (if living) to find out whether they are okay with their image cockling (which will absolutely happen with this process without overall mounting) or if a perfectly flat image is part of their artistic intent. I've had one artist who was very into seeing the print as an object who wanted the cockling visible, and one artist who wanted his prints completely flat. We had the mounting done by Erizan Inc. in New York as this was the mounter who had worked with the artist on mounting all of his Polaroids in the past. If artist is okay with some cockling, I'd go with edge strips.