RED50 - VLAN and DHCP not working

I have an internal client vlan (VLAN12) that I need to pass to a remote office.  I purchased a RED50 because the literature says, it can handle vlan’s.  Only, I’ve tried every which way that is suggested by the Sophos Community and I cannot get it to work.

VLAN12 works fine internally, but when I try to pass it over the RED50, I get nothing.  Hopefully, someone out there will be willing and able to give me a hand with this.

My current setup is as follows:

• Windows Server 2012 R2 DHCP server (10.0.0.12) on a management vlan (VLAN1)
  • Client DHCP scope setup:
    • Address pool 10.0.12.1 – 10.0.12.200
    • Router 10.0.12.254
    • DNS server 10.0.0.12

• Sophos SG310, UTM 9.409-9 (10.0.0.253)
  • Eth0 = Internal LAN (10.0.0.253)
  • Static route (gateway) - Internal interface and Client network to core switch
  • Firewall rule - Internal interface and Client network to Internal interface and Client network for Any service
  • Firewall rules - Internal interface and Client network to Anywhere for DNS, HTTP, HTTPS, etc
  • Multipath rule - Internal interface and Client network to Anywhere for Any service on the WAN interface

• HP 3800 core switch (10.0.0.254), setup with:
  • Default gateway (10.0.0.253)
  • VLAN1 (10.0.0.254)
  • VLAN12 (10.0.12.254)
  • IP route for 0.0.0.0/0 with the gateway IP 10.0.0.253
  • VLAN12 has an IP helper address of 10.0.0.12

Port 1 on the core switch is untagged in VLAN1 and connects the DHCP server

Port 10 on the core switch is untagged in VLAN12 and connects a client PC to the network

Port 38 on the core switch is untagged in VLAN1 and connects to eth0 on the Sophos UTM

When I connect a PC to port 10 on the core switch, it gets an IP address from the Client scope on the DHCP server.  The PC can also connect to all other devices on both VLAN1 and VLAN12, as well as the internet.

Without me going into to detail, I have tried setting up the RED50 in almost every conceivable manner, and none of the setups provide a connection back to the DHCP server.