Depending on the external enclosure you may have to:
1) Connect two eSATA cables to the enclosure, one for each disk, if there is two eSATA connection on the eclosure.
2) Use a special controller if the drives are to be used witj only one eSATA cable.
If the box you have the disks in have two eSATA connections, 1) is more likely.
Ronny