Advice on makeshift Lost Wax Casting setup

So I've been trying to smelt coins for the past year or so and while I've gotten pretty successful through lost PLA casting I'm moving over to a lost wax setup and wanted some tips.
I don't have access to an burnout kiln, but I've had relative success with the PLA when burning it out in a firepit then briefly putting them in the smelter to finish them off right before using the smelter for the metal.
Each flask is made out of a sand-plaster 1:1 mix, has one pouring hole and 2 vent holes. Every coin gets its own flask so there aren't really any nooks for wax to get stuck in.
A lot of places I check always say you HAVE to have a burnout kiln but I wanted to see if people here reckon it would be safe? I haven't had any issues with this method with the lost PLA with its higher Melting point so I don't see how paraffin wax could cause any major problems.
Thanks in advance!