Is this good for the external HDD enclosure

I'm thinking of buying this external IDE enclosure. I already have another one but with a sata connector so I know that that they are good, solid enclosures.

The thing is, when they run for a long while, they tend to get hot, not burning hot, but hot enough that I'm a bit worried it might damage the enclosure and the drive after long periods of time. So I thought I would use an external usb fan to cool the whole thing down.

My question is, if I plug the usb fan directly in the usb port of the enclosure, do you think this will be bad for the drive and the enclosure. I usually use firewire so the usb port is freed up. The enclosure gets its power from the power outlet, not from the computer itself.

Sorry if this didn't make much sense, english isn't my main language.

Thanks.

Also, there are two firewire ports on the back of my enclosure, do you think you can plug one enclosure in the computer, and the second one in the first enclosure?

Jam it back in, in the dark.