Heating Pad question

Im planning on getting two leos soon and I have temp housing for them, its a plastice tub, can I put a heating pad under it? I dont want the tub to melt.

Yes, that should be fine. Remember to use the little feet that come with the heat pad. They stick to the corners of the tank so the heat pad isn't against the table or desk or whatever the tub is on. The heatpad should only heat to around 95* which is not enough to melt a plastic tub.
To be safe, use a probe thermometer to measure the floor temp of the ground, to ensure the temp doesn't go too high.

you should also have some type of regulating device to control the amount of electricity that the heat pad gets. plugged strait into the wall, it will get way too hot, without a doubt. a thermostat or rheostat is highly reccomended.