Nice work Rowland, look forward to the results.
Not sure if you've come across this, thought it might give a few ideas.
He's stripped a 450D and assembled it bare bone in a custom body for sealed cooling.
I particularly like the black silica gel ring idea and the electronic shutter simulator.
its in Croation, just let your browser translate it, if you're using Chrome.
http://filiplolic.com/cooled_canon_450d/
Cheers
Alistair