I really liked your shower rod idea, I immediately implemented in on my X18D with a twist.
I put the shower rod just an inch or two below the ceiling along the wall behind the toilet and then using zip ties attached a shower curtain along the back wall on the rod, and then attached it all the way around the shower inside the factory curtain (which stinks by the way).
I let it run one eyelet long on the other end and put a Command hook horizontally that you can clip the shower curtain to. So now the curtain wraps all the way around the corners on both sides.
You could not take a shower in our shower without water shooting out the sides and even through the curtain but now you can go crazy and nothing gets out.
Your bathroom is a different setup than mine so you may not have this same issue, but anyone with a layout similiar to the X18D might want to try it out, it has really helped our bathroom out a lot.
As an added bonus, we purchased a curtain that has mesh pockets on the inside of it that are very handy for holding shampoo bottles and such.
2008 Tundra CrewMax 5.7
2011 Jayco X18D Hybrid Travel Trailer