I would suggest a locking fuel cap....a little bit of insurance....you have to actually unlock it so you are aware of fueling verses DEF......and if doing DEF, I pull away from the pump before adding any....and with the locking fuel cap, you probably won't be holding DEF and accidentally add to fuel tank....
You can get the Stand locking green cap off eBay for less than $15....10510D
Also, get the Ford DEF nozzle.....less than $7 at your local dealer or online...it fits most DEF jugs (I use Wal Mart for l3ss than $8 for 2.5 gallon jug) and fits snug in the def tube. Also stops when full and less prone to spills which can be corrosive to the paint. P/N PM-27-N
2015 F350 Ultra Lariat 6.7L CCLB DRW 3.73 Limited Slip, Green Gem Metallic w/ Caribou accent, Camper Package, Titan 65gal tank, Rapid Heat, Block Heater, Upfitter Switches, Dual Alternators, Camper Package, Cable Lock, Husky Floor Liners, Spray in Bedliner, 5th Wheel Prep, 25K 5th Wheel Hitch, Ford Goose Neck Hitch.
Traded 2011 F350 XLT CCLB SRW 6.2L gasser 6,000 miles for 2015
Sold 1996 F350 XLT CCLB DRW 7.3L 208,000 miles