+1 on the DAP Weldwood, but my experience has been that if one roughs up the foam surface (removes the "skin" it has), then it takes more that thin coats because it kind of sinks in. But I note you said "gel formula", and I don't recall seeing that before on my can, som maybe that's the diff.

I agree on the surface prep. The original waxy skin needs to be removed. Band saw cuts left a nice texture and wiping on a couple of coats of contact cement with another piece of cut foam was the standard application. My experience has been with foam to foam, foam to fiberglass, and foam to gel coat which needs a light sanding.

Thin coat is relative. What doesn't work is too much adhesive on each surface that when put together forms a fluid sandwich, that seals and can't dry, with the weakness being in the undried cement in between.

The Gel and the Original seem to be about equal though the Gel is not stringy and keeps the can lip clean. I stumbled on to it at a local hardware store and now Sterling uses only the Gel Formula for production.

For Minicell foam to Polyethylene 3M 4693 is best.