There are cigarette outlets available with caps, but I prefer the
Powerlet (BMW-type) outlets. They hold better and don't lose contact on the bumps. I don't know of anything that will fit the hole directly. You'll have to put in a plug, such as that made to cover the gauge hole on the standard RT, then drill a hole in the plug for your outlet. Don't forget that if you use the gauge lighting wires for your power that they are very limited. I would fuse the outlet separately, and not above 3 amps. If you run a wire from an auxiliary fuse block, you can get more amperage.