It looks like it was designed to work off the trailer. My original set up worked that way. I attached a block and tackle to the trailer tongue and then I had a gin pole with two eye bolt at the top, fore and aft. The block and tackle attached to one eye bolt and the end of the forestay attached to the other. The bottom of my gin pole pivots on unused holes on the front of the mast foot bracket.
I've since changed it so that the block and tackle attaches to the forestay bracket on the foredeck, and I added removable baby stays to the mast. That way, I can step and de-step the mast while I'm on the water. The launches I usually go to are frequented by power boaters and I didn't like being in the way all the time when I rigged. Now I pull and launch just like a power boat, and step the mast as I'm motoring away. I made a custom fitting on the top of the gin pole that hooks onto the turnbuckle at the bottom of the forestay. So the forestay starts out attached to the block and tackle, and then it's attached to both the block and tackle and the deck fitting, and then I disconnect the block and tackle and gin pole. Solid control of the mast at all times.
One of these days I'll post some pictures of my system.