Hi david, i use a similar method to Dougal. I make a little plasticard box that fits around the motor, put some silicone sealant in and push the motor in. I then connect a low voltage to the motor, with it coupled to the shaft. I then adjust the motor until its running sweetly, and let it set. One advantage is near silent running with no play in the mounting. If the motor needs replacing it comes out without much fuss.
One model now over 30 years old is on its third motor in the same mount, it just works without any problems, and is particularly good in plastic hulls that can reverberate.
If you do this, make sure not to get silicone over or in the holes / slots in the motor casing, and make sure the area under the motor is clean and grease free before starting.
Chas