Here in SoCal we have a collaboration project we call the "VARA FM Autobahn". It connects Ventura, Los Angeles and San Diego County ARES groups and CREBC in Tijuana. The goals are to provide area coverage, leverage mutual aid and provide access to HF gateways for potential forwarding of out-of-area messages. Regional communications are important in SoCal, so we do try to provide multiple paths for traffic through VARA FM, Packet, AREDN Mesh and HF.
The Autobahn comprises of 10 gateways, which we leverage by having every user station enabled as a digipeater with SSID -4. Not sure if that counts as a "reasonable" number :-)
Jer K4WOF and his group in Florida have similar VARA FM network supporting their mission.
73 de Oliver K6OLI