Hi Paul,
You may find this guide on setting up Web Access in a DMZ using a reverse proxy to enable Windows Authentication helpful:
https://answers.laserfiche.com/questions/92938/Web-Access-10-in-reverse-proxy-with-IIS-in-DMZ
While I have not tested that configuration with Laserfiche Mobile, the Mobile App Server is an IIS application like Web Access, and the networking-level concepts should hold between them.
You may also want to consider third-party software or hardware load balancers such as HAProxy, Nginx, and F5, all of which have reverse proxy functionality.