Thought i would post this guide which i got from Lifesize support a few years ago it helped me with a Lifesize end point install i had yesterday.
We did have an issue with incoming presentations even after following the guide to the letter. We only managed to fix the data sharing issue after enabling deep packet inspection globally then turning it off via a policy for the VC rules. Very strange since deep packet inspection was turned off globally before anyway.
Anyway hope this helps someone fighting with a Watchguard firewall