I have a fairly typical self-built propane forge with a venturi style burner (actually one of J Prices 1" forge burners). This is not my first forge/foundry build, but for some reason (for a myriad of reasons actually), I decided not to secure the burner the way I usually do (with set screws in a receiving pipe), but opted to invest the burner in the receiving pipe. Yes, this makes the burner position not adjustable (but I'm fine with that, for now).

Just curious if anyone else does/has done this, and if you had any issues down the road.

I invested it with a watery mix of satanite over the course of several days; this made it well insulated but also pretty easy to chip out if need be.

-a  

I haven't done it your way because I was concerned about heat conduction from the forge to the metal of the burner.  You may find, if not really cleaned well. that a gentle twist will free the metal from the surrounding investment. I found, in personal experimentation that the extra air  inducted around the out side of the burner tends to make the burner tube last a little longer.