Electrical plug question
You can't / shouldn't try to make an adapter to power a 6-30 device from a 6-15 receptacle, the voltage is correct but the current handling capacity is insufficient.  The 6-30 heater would at a minimum overload the 6-15 receptacle, and likely overload the circuit's wiring and breaker.  Hopefully the breaker would trip before much damage was done, and you'd only waste time, but if the breaker doesn't trip quickly, you could start a fire.