555.13(A)(2) says you can use SO cord (assuming the right grips on each end) If you needed additional protection I guess you could sleeve that in Carflex since it is a chapter 3 wiring method as stated in 555.13(A)(1), pursuant to protection in 555.13(B)(a)(5). If there are sections above the deck you need RNC per 555.13(B)(5)
