On my 37c
I recently (1-1/2 months ago) installed the mackpack on my 37c. I simply called them with the measurements they ask for on their web site and the sent me the mackpack with alll the fittings and an amatuer home video on how to install it. Total cost was $540. Installation took about 2 hours, with the most difficult being the attachment of the small blocks 2/3 of the way up the mast. With the exception of someone pulling me up the mast, I did it myself (and that's saying something !!).I really don't know how I've lived without it. No more mainsail covers to deal with, no more sail ties. Dropping the main and zipping her up takes about 1-2 minutes. My father -in-law has the mackpack on his Hardin 45 ketch, and he has it on his main, mizzen, and staysail !