The sHF 18 Field Howitzer (Schwere = HEAVY) Feldhaubitze 18 was a 15cm Calibre gun. All charges were 'bagged' - a canvas bag for the propellant charge and the shell seperate. Wicker cases were only used for some of the 'fixed' ammunition types 75, 88 etc. Charges for a 15cm would be kept (if my memory serves me well) in a wooden charge box.
However, if you're talking of the leFH 18/40 (Leichte Feldhaubitze "light field howitzer") it would certainly have these for storing rounds:
IMAGES FOR DISCUSSION PURPOSES ONLY!!!!
German 10.5 CM Howitzer Ammunition
Charge Cases:
WICKER AMMUNITION CARRIERS

10.5cm Howitzer Cartridge case box