I'll attempt to contribute.
Steel bedding, glass bedding, and "pig belly pink bondo bedding" all attempt to achieve the same end result: a tension free "nest" for the action to register to. It should be inert to ambient changes in weather as well.
There is an almost endless supply of variations of this. They range from precision castings to machined inlets made from aluminum/steel. All attempt to do the same thing.
One point I'd like to note is the use of atomized "steel" in a resin. If it is truly a ferrous metal then it is going to be susceptible to corrosion just like any other steel. I'd fear that in the more humid climates you'd end up with an orange patina over time and eventual breakdown of the casting. I'd suggest using atomized SS instead.
I use a resin designed for commercial boiler repair. If it'll survive that kind of environment, it'll take just about anything. (Hunting down inside a volcano being the exception I guess
)
If using an epoxy to make a casting, the resin should have the following qualities:
1. High Shore Hardness
2. Low percentage of shrinkage
3. Long open clamp time
4. Strong resistance to chemicals/alkalies.
5. High compression strength
6. High shear strength
7. High torsional strength (the one that's often failed to be mentioned)
Hope this helped.