I have had three mast steps on ALMA. The original one rusted. The base of the mast corroded along with it. I took the old mast step and strapped it to my motorcycle to take it to a machine shop. When I arrived it was gone! Likely it found a home in a school bus windshield... Now I had no step for a template.
Luckily a local rigger was working on a sister ship 323 and he allowed me to come aboard and make detailed drawings. I had a new steel one made and took it to a 'powder coating' shop for the "miracle of the 90's"- Powder Coating. It lasted about a month before bubbles of rust emerged.
The steel lasted long enough for me to come up with a new step that was:
1) Corrosion PROOF.
2) Galvanically benign to the Aluminum MAST.
3) STRONG enough to handle the LOADS of the 'tension rod' that keeps the bulkheads firmly in their molded pockets when the shrouds try and squeeze the hull and lift the deck from the hull when hard on the wind. I did not believe an Aluminum Step can hold these loads with the current rod- Ed's 1/2 inch plate looks robust enough- LOL!
4) Electrically ISOLATED from the mast to allow the bonding to attach to the mast and NOT trust electrical bonding (less than a couple of volts) continuity through the step.
5) Elevated off the bilge to compensate for TWO rounds of trimming the base of the mast to cut beyond the corrosion. Remember the shrouds and stays are in agreement with the original dimensions of the uncut mast. And high and dry from nuisance bilge water.
6) Strong enough to locate the mast in it's perfect position for alignment and rake.
7) Self draining of rainwater that enters through the sheeve box.

PRETTY! after screwing around with this for years I wanted an elegant solution-
I found the answer with a stainless steel step with a bi-axial fiberglas 'cup' locating the mast and electrically insulating the aluminum from the stainless steel.
A simple aluminum plate in the fiberglass prevents the mast extrusion from cutting into the fiberglass cup-
It is six years old now and looks like new-