If you want honeycombs, Plascore is a great supplier. We use their panels, as well as GFC, SuperPacific, and Adventure Trailer. Probably some others as well.
I used some honeycomb in our build 18 years ago. I would not use it again.
It was a tad cheaper than the closed cell polyurethane that I prefer, but the thermal insulation quality is very poor and the weight was higher.
Cheers,
Peter
OKA196 motorhome