Precautions in connecting high voltage source to a relay?
the Idea you have is good , but the components although "rated" for 10 amps really will not hold up long at that level. I usually only load these small relays at 50% and as low as 10% if it has a short cycle time. the problem is contacts in the mechanicial ones will soon stick and overheat your hot plate , The electronic ones the solid state relays internally short untill the junction is blown apart but usually dammaging the divice they are driving.
as for plastic it melts, maybe a plastic liner in a metal box or standoffs in metal but use caution it will probably work for a while but when it fails thats when things get ugly