Need help/advice finding INTERMITTENT water line leak

Intermittent ... won't be intermittent for long if you don't find it.

And no pipes above that water could leak down from (ice machine, sink drain etc)?

1st Visual...(with hot water fired up) again with flash light real good and slow.

2nd paper towel (rats nest of hoses) maybe wrap a paper towel and hold in place with scotch tape. Leaker will be wet when leaks starts again.

3rd Do you have a way to test rv water regulator off from rv? I use a air compressor with its own regulator and a blow out plug. If regulator is bad it could be letting water in when city water pressure gets high. If you're at a place where water pressure is high during certain times of day.

If you have an air tester that keeps check valve open during testing, it would help separate if leak is from pressure side or discharge side. And most likely find the leak if leak is on high pressure side if you air up to around 45-55. Don't discount a water leak, leaking somewhere (prime suspect is hot water heater) and drip is flowing back, on outside of pipe.

We had a similar problem. One night I found the tiny amount of dripping water was hot.

After focusing on the hot water lines, I determined that the water was leaking from the hot water heater near the upper water input.

More testing determined that the leak only occurred when the water heater was full of hot water.

Suburban replaced the hot water heater, no more leak.

Might have nothing to do with your problem, but I'd suggest checking to see if the water heater might be the source.

Check your refrigerator (if it's close) ... both defrost and icemaker.

The defrost line has a nasty habit of plugging up. And the plastic icemaker line has a nasty habit suffering from a pinhole (or slit) leak so small it's a fine mist almost invisible, but if you put your hand around it you'll feel it.

possibly a shower or sink drain

I had an intermittent leak. Was created by high pressure in the closed system. High pressure was created when the water heater would go from full cold to full hot with no water use to relieve the expansion. After fixing the leak I also added a small ShurFlow expansion tank.

Rarely does a flow water line leak intermittently- it leaks or it doesn't. I have to wonder if your water leak wasn't coming from another source, perhaps water splashed from a sink or shower.

First thing I would do is switch to the water pump - even if you have even a slow leak the water pump will periodically turn on as pressure drops. If the water pump never turns on then your issue is likely related to water pressure or maybe rain etc. Doesn't help diagnose a fitting which won't handle higher pressure but will help eliminate possibilities.

My buddy had a hard to find leak. It ended up being a tiny staple poking the tubing from underneath. Had to run hand along all the pipes to find it.

Also, if there's a vacuum breaker for the black tank rinse, it may occasionally spit water. (Mine never hase but others have reported seeing this).

Finally, some outside showers have a weep hole on the back of the valve that will let a litte water go after use.

Yes, I was using a pressure regulator then and now.

Were you using a water pressure regulator. Thinking perhaps too much pressure. You might try putting newspapers around then shaking the pipes to see if anything drips.