Water intrusion into power compartment on 2009 Itasca Meridian

I am having a water intrusion problem with my 2009 Itasca Meridian. It all started several years ago when the original (Dimension) inverter burned out. It was replaced with a Magnum unit of the same wattage but a different physical size. Since then it has had to be rebuilt twice because of water getting into the inverter.  The unit is located just behind the driver side rear wheel on the side wall that divides the wheel well and the compartment.
The first time the new unit failed the dealer who did the change out, resealed the compartment and said I was good to go. That turned out not to be correct. The next time I drove in the rain, water entered the inverter again, I returned to the dealer and they rebuilt the inverter and resealed the compartment which they did free of charge.  But the next time I drove in the rain, once again the compartment leaked, and I noticed the water before I plug in the inverter so it was not damaged. I returned to the dealer and they put the shop foreman on the project this time. He again resealed the compartment and off I went.
This past weekend I again drove in the rain and again I had water in the compartment. Thankfully I found the water and dried the area before plugging in the inverter. The water seems to be coming in just above the inverter, it then runs down the wall into the inverter.
I know the shop has run sprinklers overnight in the area without leaks, they have resealed the wheel well and the compartment several times, they even added a little mud flap to help protect the cord outlet door.
I?m more interested in seeing if I?m the only who?s having this problem.  Does anyone know a fix?

But a bright LED light in the compartment at night and close the compartment - look for light leakage. I have a marine bilge blower under our bed that forces air into the electrical bay compartment which helps pressurize it but we still need to cover the power cord flap thingy with a towel to keep water ingress out.

It really depends on how/where the water is entering, but I have used spray undercoat to permanently stop compartment leaks ...I cleaned the outside of the compartment, hand sealed with silicone caulk every seam, screw or hole I could get a finger to, and then sprayed the undercoat liberally onto every area the spray would reach, especially those tight spaces I could not reach with my finger of sealant.

https://inspectusa.com/180-minute-smoke-test-pen-kit-s220-wick-refills-white-smoke-p-237.html?utm_campaign=Smoke2520candles&utm_content=Smoke2520Emitters&utm_medium=cpc&utm_source=bing&utm_term=smoke2520bombs  Try this to find your leak.
We used to use a similar device in automobiles to find leaks.

gwcowgill said:

https://inspectusa.com/180-minute-smoke-test-pen-kit-s220-wick-refills-white-smoke-p-237.html?utm_campaign=Smoke2520candles&utm_content=Smoke2520Emitters&utm_medium=cpc&utm_source=bing&utm_term=smoke2520bombs  Try this to find your leak.
We used to use a similar device in automobiles to find leaks.

Click to expand...

Works in some situations, but not a fail safe. I had a fairly severe leak in a storage bay under warranty.  After many attempts at sealing it by several dealers,  the last one told me "we smoke tested it & it is sealed." When I got it back to the rv park I ran a water hose on top of the compartment & it immediately leaked.  I took it back & told them "I don't have a problem with smoke getting out ... my problem is water getting in."  They finally dropped the entire compartment & sealed it properly. They screwed up one of the compartment ceiling lights & I had to disconnect the hot lead to the two lights to keep a 12v breaker from popping  but at least they fixed the water leak problem. No lights is better than water leaks!

Thanks for the replies, great ideas..
The problem occurs only when driving down a water covered road in a rain storm... So it has something to do with the water pressure caused by the wheels throwing the water up..  I know they have caulked and undercoated all around the back part of the wheel well.. Anyone done a water pressure test in the wheel well?

It's very difficult, using sprinklers and hoses, to replicate the conditions of driving in a heavy rainstorm. Aerodynamic forces change the way things seal. We fought a water leak in one of our helicopters for the longest time before discovering why it was leaking.

You could squirt pressurized water at it all day, from any angle, while the aircraft was on the ground, and it wouldn't leak a drop. At 50 knots and above, however, rain would get past the door seal - even though it wasn't directly hitting the seal. We finally realized that low pressure, that exists outside the aircraft in forward flight, was pulling the door outward, ever so slightly, away from the rubber door seal.

There's a similar low pressure environment on the outside walls of an RV as it moves down the road. I'd look real hard at the basement compartment door seal, to make sure that it's flexible enough to expand adequately to stay in contact with the compartment door, in case it's pulling away from the seal as the RV rolls down the road.

Kev