STUN SERVER how can set in FREEPBX

I need to use Stun server of Clouditalia in my PBX System, because is the only method for make work my inbound number.
If i not use Stun server never work.

How can i set Stun Server for CloudItalia trunk in a FreePBX system?

the stun server that i must put is:

MY ISP Block 5060 port because the same ISP offer a VOIP Solution integrated in the router.
If i use X-Lite, Ata Adapter and other things… the cloud italia account register correctly and receive calls only if use STUN SERVER.

So i must put this in my PBX System… but i don’t know how. I try thousand of methods… but no one works.

Someone can help me please?