1980 Airstream Excella II Water Holding Tank Questions

[jmlitch99]

We are in the process of renovating our 1980 Airstream Excella II and more specifically doing the plumbing. I have a few questions specific to the water holding tank and would love any thoughts, tips, recommendations on the questions below. Thanks!

1) The underside of our Airstream below the tank is rusted out. We need to fix this but also want to ensure we still have an access door/hatch so we can access to the tank drain. Would love any tips or recommendations for creating a door/hatch for accessing.

2) The plastic piece for the inlet for our water tank is broken. See attached pic. Would love any recommends for an easy fix of this.

3) On the top of the water holding tank, there is a piece that screws into the tank. See attached pics. What is this piece? Ours is broken and I need to replace it, but I not sure what the part actually is.

4) We would like to install a digital system for monitoring the water level in the tank. Would love recommendations for a good system.