Just an FYI, we received a few CORETec 'original' samples last week. They looked really nice, both inside and out. They were WPC (wood plastic composite). If were weren't expecting such temp extremes we'd probably have gone with that. As it is it may still be suitable - it is warrantied to 140F - but we want to minimize our chances of failure as much as possible.
Yesterday we went to a showroom to check out the CORETec 'Pro' line, which are SPC (stone polymer composite). They looked awesome as well, and from my research, SPC construction (which can be had in other brands as well), appears to be the best bet for dimensional stability across wide temp ranges. Less give so less comfort, I understand, but that's not a big concern.