Hi,
I’d created pretty comprehensive checks for pfSense/OPNsense a while back.
It works with both flavours of the BSD firewall distros, and has adjusted haproxy monitoring, squid, updates etc.
I’m also interested in merging these so in the end there can be a proper OPN package that one just installs from the package management.
Would be nice to work on it together, but if it’s faster for you, you can also just grab the pieces you need.