Help (long)FW plumbing leak

[Poper]

I have inspected and sealed even where not needed all roof penetration, no water anywhere in coach at all.
My floor insulation is soaking wet. I have an enclosed under belly, so this PEX FW leak may have been happening for some time, but after checking several locations aft of the axles it’s really soaked between the coroplast and the floor.
My question: I just purchased an air connection with attached guage specifically for plumbing leaks. It will attach to the hose thread FW exterior connection. I know there is a 5psi check valve in there too. Can I put say 60PSI since PEX is rated 100 psi and watch for a pressure drop? Then find the leak using soapy solution. There is no evidence of leak in coach anywhere I can access through panels etc, so assume it’s under the floor in the enclosed belly.
I’ve had the coroplast down, but the plumbing where it’s not exposed in coach runs above that in the insulated areas,with the black membrane mesh is. I need to drop coroplast, black and gray tanks, remove all insulation find and fix the leak and install all new. Is this doable? I’m retired home builder with skills, tools and time. Wits end and a little apprehensive. Assume RV dealers must pressure check RV plumbing somehow. Any input or advice or previous experience greatly appreciated Thank you

[wvcampers]

is it possible that you have a drain or a tank leak since you have not seen water running or dripping from the coach? Most FW leaks would be continuous when the water is on and you should see water dripping somewhere. Check the shower area too.

[valleyduo]

We forgot to winterize an outside hose port once and the pvc extension on the back of it cracked. Guessing you probably already checked it, but just in case.