It's not overkill. Granted its on a river stretch, but the rubbing strake will absorb scuffs, but in my book a couple of fenders is best practice.
All my fenders are basically fishing bouys that have been lost at sea and found as flotsam and jetsam. I tie them on the back of the second jockey seat and deploy in the harbour. On your boat, space will be a premium, so some Plastimo flat fenders are lightweight and would do the job.