Animal Plastics--they're very sturdy, the routered-in heat cable is sturdy and reliable (better than Flexwatt in that regard), they're less expensive, and they hold heat very well.

You can get rolling castors for them, as an option.
The sole drawback is that they often have an order backlog, and it can take 4 to 6 weeks for them to fill an order in some cases. Well...they have a backlog because they're popular, and there is a reason for that.