[BestPractices] Have any of you ever had to secure access from WAN/WLAN->Cellular Gateway<-IOT ?

If so, what intermediaries did you use and why and how?

I've done my share of network provisioning, but the most I've done with cellular stuff is directly related to failover/HA and I'd like to know how that sort of things works a few years on from my experience now that technology has advanced.

I was thinking bluetooth mesh and VLAN'ing networks, since bluetooth is more graceful about travel than WLAN is with regards to access points, but this is new territory for me and I haven't really read up on anything aside from just the base of the technology itself.