If it's a weather leak it gets harder as we have such a hard time getting weather to test and spraying water is not always the same as letting snow set and figure how to get in!
If you want to go to a bit of trouble, testing for a pressure water leak can be reasonably simple if we get the right parts on hand. One problem with slow leaks is that they can do weird stuff like set and pool on top of something, so that we don't see it and then when we move the RV, we suddenly get a tub full of water coming down somewhere.
So to get a better idea of whether we have a slow leak we can set up a pressure situation.
If access to a faucet is available, a small water pressure gauge can be worth buying:
Addd this to a wye along the line from the faucet to the RV, Keep all inside faucets closed and not leaking, then turn on the pressure to get what your water pressure is. This makes the meter flip up to record, then turn the pressure off. This leaves the pressure reading isolated between the faucet and RV, so we can go off and come back later to find if the pressure has dropped. This does require that all the faucets and connections involved have to hold good but if the pressure drops very much, we can say we have a leak and most likely in the RV fresh water system.
The $15-20 dollars? Yeah, I'll do that to know for sure where the bear is hiding!
Good luck to you as it's far easier to set here and write about it than to solve the problem.