Puma Ginger Beer,
JSP 752 explains all, I gained access through ArmyNet, I guess your service has an equivalent. I quote....
INELIGIBILITY
03.0115. Ineligible Personnel. Subsistence is not payable in the following
circumstances:
b. When Service personnel are living under Field Conditions, no matter
what the type of accommodation, there is no entitlement to claim either
subsistence or IE.
Not what you wanted to hear but there you have it.
SL