Hi there,
I see what you are trying to do ... but the problem is traffic will never route to your loopback address and will never get translated. You will need some policy-based routing to push the traffic to loopback and then once translated push it out to the external interface and use IPSec tunnel.
I can have a look at it for you, please let me know when you are available for a quick chat.
Thanks,
Shahzad