if it is just for storage, they should be fine, just make sure you don't have any leaks, or you will have 5 gallons to clean up in the fridge...
if you plan on carbonating while they are on their side, i would highly recommend getting inline check valves for the gas line, as it is easy for beer to back up in to the line and possibly destroy your regulator.
Walk-In Serving(14): Oatmeal Stout, Hard Cider, Belgian Tripel, Liquid Stupid, Belgian Dark Strong, Red Bull, Rye IPA, Double IPA, Imperial Stout, Irish Red, Scottish 70/-, Belgian Wit, Nut Brown, Traditional Mead
Walk-In Cold Storage(~50): Cysers, Braggot, Melomels, Ciders, Traditional Meads, Persimmon wines, Dry Stout, barleywine, cream ale, sodas, Chocolate stout, milk stout, and others I can't recall.
Fermenters (0): Nothing current.