Hi!
I asked myself that question this summer when i was about to test fly my 26-27 year old Marutaka DC-3.
This airplane's fuselage is mostly covered in many small pieces of chrome Oracover and has Flite-Metal (or aluminum duct tape) on engine cowls, tail-cone and lower fin and on wing fillets.
The JR receiver (R 700)I used is mounted inside the fuselage with the antennae all inside the fuselage (it's not hanging out from the fuselage).

I checked how far I could walk with the transmitter fully collapsed, pointing at the model, many times before the first take off as I was a bit reluctant to weather it would work...but I had the same ground range as with all my other models (100m with antennae fully collapsed and pointing at the model) so the first flight went just fine and there hasn't been any range problem since either.
Weather a model fully covered in Flite -metal would have problem is something I really don't know.
Regards!
Jan K