CARP IP Failover based on LAN device availability (like Gateway IP monitoring)

[dave10x]

Hi All, I have a scenario where I have two pfSense boxes hosting public IP's using (CARP) each one of these has a router / content filter attached to the LAN side of each on separate networks with two more pfsense boxes doing MultiWAN failover using a shared CARP IP for the LAN client Gateway.

CARP Public IP --> pfSense01 --> Contentfilter --> pfSense03 (multiWAN) --> CARP IP (GW IP for LAN) --> LAN Clients Network A
CARP Public IP --> pfSense02 --> Contentfilter --> pfSense04 (multiWAN) --> CARP IP (GW IP for LAN) --> LAN Clients Network A

I would like to be able to monitor the content filter IP's on the LAN side from PFSENSE01 and 02 and if one of those fails then move the Public CARP IP to the failover PFSENSE similar to the Gateway monitoring that can be done with MultiWAN failover.

I cant see a way that this is possible unless anyone has a better way of doing the above. We are on a budget mind.