So this is how it played out.
OpenPark and Wolf-guard were a bust. Both European companies and have no online purchase presence. Wolf-guard never responded to my email and OpenPark was only interested if I was interested in being a US distributor.
Zipato did not have very good reviews on Amazon at least relative to Smartthings integration so I skipped it.
Ended up getting the Aeotec. It works very nicely in my heated enclosure. The siren is a lot smaller than I expected so it easily fit with room to spare even with the hub already in it. Although the enclosure dampens the sound somewhat , it was more than loud enough for my purposes.
You do have to install a custom DTH [RELEASE] Aeotec Siren 6, and will likely want to change the default siren sound and volume to get the loudest possible siren sound.