I generally don't let my DEF level get much below half. In the fall after a summer of traveling and I know my RV will be sitting for 3 months or so in Florida I try to leave it less than half upon arrival. I then top it off a week or so before traveling the in the spring.
Full Time in 2017 Newmar Ventana 4369
pulling a 24' enclosed (Mini Cooper/Harley/Kayak)
(traded 2014 Thor Challenger)
US Army 70-73 Retired LEO