The rule of thumb I was told when we first started RVing 20 yrs ago was to fill the tanks before winter storage. This would prevent condensation & corrosion from developing on the inside.
With the newer tanks that can only be filled to 80% the rule does not completely apply.
I guess you are still protecting 80% of the tank.
I for one fill my tanks for storage just because thatís $$$ I donít have to fork out in the spring when Iím getting everything ready for the season.
Dave, Judy & Daisy May
2010 Sierra 356RL
2011 Silverado 2500 4WD, LT, Ext Cab, LB
Duramax 6.6L V8 Turbo Diesel
Allison 1000 6-Speed Automatic Transmission