I bought a nice H/T roll around rack from an ebay seller. He lists them in Alfa and M/B ads, but they are generic and will hold about any small H/T. It is a bolt together kit and comes with a shaped cover, so you can cover the top during storage. I had a photo of it but have since deleted it. It cost $100.00 and I can't remember if the shipping was included or extra. It has a sloped bottom and is padded so the top fits back side down and is well supported. I sold an extra H/T I had but refused to include the rack, since my recently purchased Quad also has a H/T and I kept it for my own use. Expensive but well worth it. Steel construction and 360 degree casters on all 4 corners.
Search "hardtop" on ebay if you are interested. I highly recommend. "Found it on ebay search : "Alfa Romeo hardtop" $99.00 plus shipping.
Where are you? I have two of these top storage rollers, and have sold my silver Quad, so need only one for the remaining 1959 102 Roadster. If you're close enough to pick it up (not likely, I know), then it would be a good deal for you. I'm disinclined to take it apart and find a box to fit it into. I'm in Carson City, NV. If you're somewhere in northern California or similar we could make it work.