If i stick the uth on cement floor and but a plastic tub over but leave space between for air circulation will it be ok im just trying to breed crickets for my bearded dragon and my leopard gecko just asking
Yes, it'll be fine. I'd strongly recommend using a dimmer switch, rheostat, or thermostat though.
Having said that, next time I'd recommend starting a new thread for your question rather than bumping a thread that's nearly a teenager.