Ive done this many times over the years and I can identify with your frustration. Multiple exposure has always worked. Timing the exposures is very important for success. Remember that the full moon is reflected sunlight so you need to treat exposure of the moon as you would normal exposure under daylight conditions ( IOS 100 film will record the moon fine at 125thsec at f11-16,as an example). Its important to make your first exposure at the right time for the landscape portion of the photo as this will determine how well the moon records over the first exposure. Underexposing the first exposure maybe 1/2 -1 stop will help as well. I usually wait untill the sun has set and watch the overall light with in the scene to determine when and how exposure takes place. There seems to be that majic moment when the light is just right. If the sky portion of scene is too light the moon will wash out. As far as getting the reflection of the moon in lake to regester without losing the other elements in the photo, I think may be only be achieved in the darkroom. A single exposure here may be all you'll need followed by lots of darkroom prowess under the enlarger. My first successes were achieved this way. Goodluck and let us know how it works out!!!