Just because something can be done doesn't mean that it should be done. The proper way I think this should be done is to have a qualified electrician rewire the box so you have a dual breaker, half on each phase, so if there is a fault, all power will be removed. Because of the load being 16 amps which is the max continuous recommended for a 20 amp circuit and breaker, I would suggest using a 25 amp (or 30) dual breaker, #10 wire, and a proper 30 amp outlet. Check with an electrician to make sure this would be what is recommended or required by your local electrical code.