Jay,
Silicone tube will work of a fashion but will tend to cool the air around the motor not the can, and not very well at all.
What in effect you are trying to make is a heat exchanger where the heat from the motor flows into the WATER in the cooling coils.
Silicone doesn't transfer heat readily so the exchange of heat is very inefficient.
Brass, copper and aluminium being a metal have a far greater ability to transfer heat (thermal efficiency) so are far more efficient.
It is rather like putting a towel over you home radiators, they will still work, but take much longer to work effectively.
If the motor is getting hot you want to remove as much heat as possible as that is dependant on the water flow through the pipework and the transfer rate through the pipe walls.
You can get ready made aluminium cooling coils for 3 series motors off eBay for less than a fiver.
Hope this helps.
Bob