The fill hole for the water tank was installed in the rear wall of the RV, which made filling difficult with bikes on the bike rack.  I removed the fill assembly and capped it:

Next, I drilled a 3.5” hole for the new fill assembly.  It was one of those “I really hope I don’t screw this up” moments:

New fill assembly added:

On the inside, I opted to add a second water tank (the new one is the one towards the top of the photo.  The fit is very snug, so I couldn’t use the new tank’s fill connecter.  I cut it short and plugged it with a swimming pool freeze plug (looks like this):

The new tank fills using the pump supply line, so it fills slowly.  I therefore moved the fill level sensors to the new tank.  There was a great deal of plumbing to be done, but it’s all working very well now.

I also added a lengthwise support so I could split the lower bunk’s “floor”:

I did this because the lower bunk will now have a narrower mattress so that we can install floor-to-ceiling shelving for storage:

All done!