Setup BGP on F5 GTM using a loopback

You should be able to create a non floating self IP address on each box and use it as the loopback.

Are you GTM and LTM separate? If so, I'd create two other VLANs and use those to communicate if you're not using your transit VLANs.

Also, self IP's are associated with VLANs and VLANs with interfaces so you'll need to create a path from the interface to the self IP address.

Let me know if anything doesn't make sense.