OK - I'm the master of the cheap mod I admit, but found a weatherproof 12v outlet at walmart for $8 or so
Has a nice springloaded cap, and mount. Used zipties to mount it to the triple tree right next to the ignition. Worked like a champ, and can't beat the price.
Another alternative if you want to flush mount something in a plastic panel - Harley (don't shoot me) has one for $20 in dealerships that is designed for their touring models. Works like a charm, and a piece of electrical tape easily covers that pesky logo on the cap!
Edit - I have a C14, just noticed this was related to the C10. May still apply though, just need different mounting location I suspect... My apologies