Devcon steel or aluminum based putty or liquid. It costs a bit more but is worth it IMO. This stuff is solid.

Brownells also sells a kit named 'steel bed' that is pretty much the same thing as Devcon.

Bedding with a steel or aluminum based epoxy is the next best thing to an aluminum bedding block.

BTW, about the best release agent for bedding a gun is paste wax. Such as Minwax paste finishing wax or Johnsons paste wax. Both are available ar Lowes or Home Depot. It releases much easier than the blue release agent and is much easier to get off your rifles metal surfaces. Either wipe on with your finger or use an acid brush. I prefer the brush.