How do I seal a portable air conditioner?

I'm preparing to buy this portable A/C to cool my sealed flowering room.

http://www.hydrofarm.com/pb_detail.php?itemid=8482#

It says on the items description that

This unit does not contain a sealed compressor and a small amount of room air can be exchanged through the exhaust port

Click to expand...

I've seen people talking about sealing A/C units to make them more efficient/cut down on c02 leakage.

Should I buy this one and seal it or is there a better portable A/C I should be looking at?

Anyone? I have to buy an A/C today and I seriously can't find any info about sealing these things.

I've seen it talked about, just never seen a DYI or anything.