I think it possible to do submersion cooling with HDDs but kinda conflicts with having raid 5 storage. Totally defeats purpose of redundancy.
If you put it in an enclosure around HDD the problem is you will still transfer alot of heat from hdd>air>enclosure.
http://www.svc.com/lhd-v05-uk-19.html.
*For submersion cooling*
Buy 5 of these. Remove faceplate and build a new faceplate and back plate. They already have a bottomplate so just seal it airtight.
Doesn't work out you can still use the enclosures and use some foam and the drives should stay pretty silent.