I used a "Desk Stand" You know the kind you usually put on your desk to give you an extra shelf. You can poke some holes through it where your bottom fan intake is if you really want... but it's not all that nessersery Just elevating it off the carpet is the main thing.
P.S. The frame might hold but on carpet those castors are useless... they'll break under the weight, sides of the wheels will snap off. If you still want it, get some metal castors and it'll be fine.