RE: TF GS P47 Build - yeah another bloody one!!
the capacity of the pack is not the issue. You simply need to have seperate packs for RX and the light.
In fact you should have 2 packs on your RX for safety anyway.
Just use a seperate switch harness with a seperate battery pack for the Maglight - you can always use the signal wire from the rx to drive whatever is switching the light but have the power coming from the 2nd pack. If your not electrically minded it may be a bit hard to grasp verbally. You need to have someone show you, it really is easy to do though.
cheers
Peter