A simpler mod would be what I (and others) have done.
Find the thread on the "Ultimate Water Transfer" solution. It's a bridge that is installed in the plumbing that allows the existing pump to be optionally used to draw pressure at the existing city water inlet. Conversely, it can also be used in "stock"mode, for when you have a pressurized city source. This requires no additional thru-wall or floor modifications, just a pipe and a hose cut, inside the TM.
To fill the TM while the shells are down, if you've made that modification, you can add a hose attachment to the high-pressure drain under the TM, and utilize that and the bridge to fill the entire water supply of the camper, all with the shells down. Again, this is a minor, reversible modification.
Start at post #25:
http://www.trailmanorowners.com/foru...=bridge&page=3
Here's a picture of the mod for the drain:
http://www.trailmanorowners.com/foru...7&postcount=10