In your position I would probably go for the caravan park at Benderloch (Tralee) they have chalets for rent, secure parking beside the chalet and a good private slip with trailer parking that puts you straight into Ardnamucknish bay just beside Connel.
Its about a 10-15min drive to Oban and about the same by RIB. The water distance is about 2/3rds the road distance.
If you boat was slightly shorter you would have been welcome to stick it in the drive and stay in Oban itself but its just a shade long for the available room.
There are vistors moorings at the Yacht club but they are £12 a night and I am not sure on availability.
When are you coming up? I may even have my own boat ready by then........
if you need slipway info etc drop me a line.