I store all my duck floaters in bags in the loft space above my garage. The bags are laid on their side to attempt to prevent damage. Sillhouettes are strung by stakes and hung on wall. Goose floaters get stacked in a pile about four high to minimize damage. Shells are also stacked near back, with the heads in decoy bags. I only have a couple dozen fullbodied geese and some are bagged and some not.
I've found some damage, especially to duck keels when storing this way, but laying the bags on their sides and not stacking them seems to do alright.
I've only got about 800 or so dekes
, but that is too many to build shelves for, so it's up and down the ladder multiple times for me.