Thanks for posting your question here.
The Weber Summit Charcoal Grill is new, but looks like that it doesn't have a lower damper or vent for you to mount the blower. Could you show us a picture of where do you want to mount the fan? For other Weber Grills such as Weber Smokey Mountain, you can mount the blower to its lower vent, using a silicone gasket or aluminum tape to seal the gap.
This Weber Summit Grill has a air insulation layer, I guess a 6.5 CFM blower will be enough to maintain 225 degree F. Or do you really mean 225 C?