Water line leaking

[Dav L]

Very unlikely tanks have to be removed.
Ya just need to isolate where the leak is and fix it.

Likely a line. Is your RV plumbed with CPVC or Pex tubing? If CPVC, you can tie into the old system with a fitting to convert to Pex which is easier to install.
CPVC gets brittle with time and when frozen shatters.
Small leak or large? If large, likely shattered line. If small, maybe a fitting.

I like the air pressurization idea. Listen for hisses to find the leak. Don't pressurize the tanks... they aren't designed for any pressure.

[FatChance]

If you try the air pressure test, have a spray bottle of soapy water to test suspected leak sites.