May not work for you, but my 2008 has a 3 position switch on the dome light. ON until a timer drops out (about 5 minutes) AUTO = on when the door gets opened, etc. and OFF that keeps it off all the time.
2008 Ford E-350 Quigley 4x4 V10 - 164,000 miles
RB50, PH Top, Dual AGM Group 27 Deka, 2000 Tripplite Inv., No Propane or Water Systems
Van Weight 8,100 pounds, added one rear leaf spring, BFG AT KO LT265/70R17 E Tire press 50psi.