I recently shipped an Alfa hardtop from Memphis to Richmond. I could not use a standard pallet because the top was larger than the pallet and the overhang placed the top in danger, in my opininon. So I built a crate which was pallet like on the base, which was 52 inches by 52 inches. Then I built sides and a top which were not fully enclosed, but mostly so. It ended up costing me over $100.00 to build the crate using new materials. I screwed the top to the base using lag screws through the main J hook attachments at the rear of the window openings. I built a stand on the front end and tied the front of the top to the stand using nylon rope over the front latches. The cost to ship was $266.00. This was for 135 pounds of crate and 70 pounds of hardtop, but the shipping Co was more interested is the volume of the crate than the weight. I shipped by UPS Freight because they were $100.00 cheaper than a regular truck shipping Co.
There it is in a nutshell. Top arrived safe and sound. Your biggest problem is that most sellers will not be willing to go to this much trouble at no charge to you, and if they take it to a shipper who charges to build a crate then the crating charges will probably be so high that it will break the deal unless you get the top at a bargain price. I built the crate for free, but that is just me.
Robert Hill in Memhis, TN