Having recently stepped the mast on MingMing 2, here are some thoughts.

The mast is light enough for one person to lift, but certainly not light enough for one to man (person!) handle into position. 

We had a mast crane with four of us..a bit overkill. It took quite a bit of jiggling to get it into place and lined up. So what would make it easier. 

At the partners.  I am wondering if an oval shape would be a good idea, you can then post the mast through at an angle.  The front and sides would be as with a round hole, with the rear extended.  Obviously you are going to need a giant wedge at the rear, though with the main forces to the front and sides, this should not be an issue.

Below deck.  To help guide it into the base. Fit full height boards to the front and sides.  The sides follow the edge of the partners and slope gently into the base.  The front would have a bigger gap at the top to accommodate the mast as it is angled in.  

At the base.  My mast is held down with a through bolt, an aluminium plate to the front, and an angle plate to the rear.  It was a real fiddle getting ever perfectly aligned to pass the bolt through. If it had used angle plates front and back, these could be both lose, fitted to the through bolt, then bolted down. Also, grinding a point on the bolt end would be wise.

I think with these changes, I could possibly step the mast using a simple on board gantry, without having the expense of needing a Marina.