30qt RUB; which heat pad

First off, is a 30qt rubermaid good enough for an adult BP, if so, what would be an appropriate size for a heat pad?
30qt= 22.8" x 16.7" x 7"

Also, I just checked on the "zoomed" page, and apparently only the 4x5 mini is suitable for plastic for the bigger ones are only meant for glass. Is that true or simply an over cautionary procedure?

Thank You

You would want something that covers around 1/3 of the bottom of the tub. You can use the others with a plastic tub as well, just make sure to use a thermostat to control the heat. If left to run full blast without thermostat you could cause damage to the tub or the snake.