This Method is NOT Suitable for ABS.
However for PLA running at 50 - 60 C this method will work reasonably well.
The big issus is that 12 Volts is simply not enough to generate the heat output required at any reasonable current to power the bed above about 90 C.
The Voltages, Currents and Heat Outputs we are talking about here are more than enough to Burn your House / Shed down as well as burn your fingers.
If you do try this be VERY CAREFULL !