So I remember last year at the Snoverland Expo talking with Sierra Expeditions about Howling Moon RTTs and how they ran them without the rainfly because they were so weatherproof. Last trip I decided to take mine off to make setup and teardown easier and to be able to actually use the stargazer feature now that the weather was starting to warm up. Well, last weekend was the test because there was a chance of rain. I figured it probably wouldn't rain because it's Vegas, and even if it did it wouldn't be too bad.
Well sure enough it rained pretty steady for several hours, but thankfully no crazy pounding rain. I did have to zip the canvas closed on the roof and windows as the rain hitting the mesh would splatter through. I ended up leaving the tops of the side windows open along with the front and rear door. There was a small wet spot on my pillow that I'm pretty sure wasn't drool but was from a small drip off one of the tie backs for the stargazer canvas cover. The tie back material is PVC like the cover, which means that material won't swell and seal shut when wet like the canvas material on the rest of the tent.
Water did end up pooling on the overhang, which it has before with the fly on. In all fairness I did not stake the front lines out which would hold the overhang a little more taut, but there still would have been some water pooling. My only concern is a snow trip and having a heavy snow load there. Since it doesn't really snow that often in South Africa I'm guessing they've never thought about a snow load support bar before so I guess we'll see what happens the next time I go when it snows.