I thought of that, Russ. A covered trailer is twice the money, though. If I could find a good used one that would probably be the way to go. Used ones seem to be snapped up pretty quick when they come on the market.
Harbor Freight (North Plaza Shp. Ctr. @ Perring Pkwy. & Joppa Rd.) sells a trailer kit about the size you want. Some plywood and hardware and you can enclose it and put shelves inside for multiple layers. Cost probably under $400.00 for brand new.
Just make sure it has standard spindles and bearings.
I bought a Home Depot inported special 10 +years ago and had a hell of a time finding bearings and races for it a few years ago. This year I bought a new axle and hubs so that they are standard 1" bearings and replacements for maintenance will be easy.