You may be right on the opening in the back wall. However, there was no opening in my 2014 Vegas and I never had a problem. In addition that compartment behind the shower is not closed. The pipes run along a compartment that goes to the water tank area on the other side of the coach. If you make sure that the top of the shower enclosure is fully caulked and seal the bottom, it seems like there will be less chance of water getting in there. Even if it does there should be enough ventilation for it to evaporate. That shower was not designed just for the Axis/ Vegas, so the fact that there is a hole there does not necessarily mean that it was planned for this coach. I am not saying that I know you are not correct. It's a good question. The other hole under the sink does not look like it was planned. It is just an unfinished hole.
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