pugetsystems sells oil pc kits, i think one of the tech tv shows they had the hosts build one and there was oil everywhere. I watched a bunch of videos on it. It be a good idea if you never planned to take it out again, and if you could seal it entirely shut so it never spills.
Lessons I learned
#1. Make sure it works before you pour the oil in, if you dunk it and then have to replace a part it may never get a clean connection wil the oil being non-conductive and in all the crevices of connectors ect,.
#2. Oil likes to climb cables overtime, if you can mount an I/O panel w/ sealant it would probably best, but it would have to be resistant to the oil breaking it down over time =| Otherwise you might need a drip tray underneath.
It would definitely be cute though could throw in a bubbler and maybe some toy fishes, and some EL or cathode lights.