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): Flanders red, Hard Cider, Belgian Tripel, Liquid Stupid, Wee Heavy, American Brown, Rye IPA, American Amber, Imperial Stout, Dry Stout, Cream Ale, Belgian Wit, Traditional Mead, Oatmeal Stout
Walk-In Cold Storage(~50): lots of beers, meads, and ciders
Oak Barrel: Flanders Solera