OSB, I don't think heat should be an issue, I found it the other way, where the heat from the headlight bulb was burning out some of the LEDS on the multiple LED bulb, But I have not tried a high power one, which would give off more heat.
Paul, I don't think they are canbus bulbs, my car does not have that feature, so I cannot say, but I am fairly sure they are not.
It is possible to get them, here is a much more powerful version, but if you read the small print they are not Guaranteeing 100% canbus compatability.
I think this might be too bright for a sidelight.
http://www.hids-direct.co.uk/501-w5w-extreme-power-5w-cree-smd-canbus-led-bulbs-white/