Sorry to take so long to post a reply, but have been unable to log on aat work for some reason! Hmmmm! I have fished Rimrock quite a bit over the years with a good deal of success. Typically the fishing starts in late May and goes until the water level drops. In May and June when the fish are shallow, use a wedding ring or Rimrock special tipped with maggots. A single split shot or two is generally sufficient weight to do the job. Often times it is windy enough to just drift along, letting out perhaps 30-40 feet of line. As the weather warms (about now) a deeper approach with some type of small pop gear may be necessary. Again use a wedding ring, Rimrock special, or red whitefish fly tipped with maggots as your terminal gear. Troll just fast enough to make the blades rotate, or if possible drift. Some choose to still fish with red flies tipped with maggots suspended under a bobber. I have always found the best fishing to be in the eastern half of the lake. Just a couple miles above Rimrock is Clear Lake. Give it a try as it can be very productive for rainbows in the 10-12 inch range, right about now. Troll standard stuff, F4 Flatfish/Roostertails/Wedding rings.
Good luck. Let us know how it goes.