Over night we had Misty rain and this morning the area right behind the wheel well is dry but the very back corner where it drops down had about 1/2" of water in it

This always gets filled with water but and can stare at it and never see where it comes from. I have tried using a snake camera in the C pillars but haven't seen anything

 

I think I might have solved it, I could see a tiny stream of water down at the bottom filling the hole there. I had my hose on very slow dripping over the driver's rear corner. I took off the tail light and trim and cleaned up under there and sprayed water with a spray bottle and was getting a little inside.

 

I hope that's it.

 

Can you please elaborate?

If you want to be sure that's it, then put a bit of dye in the water.

I would consider making a drain hole in that area where the water pools up. Then stuff some filter foam in it so dust doesn't get in.

 

How do you access this tube? I live in a rainy area so I need to be proactive about such things.

 

After drying out the recessed corner inside the van, I got a spray bottle and starting from the bottom sprayed a stream into the seam that I have the arrow pointing to. Just below the hinge was a good opening and as soon as I started spraying there water was streaming down into the inside corner in the van. I got white silicone and caulked the entire seam. I took the other side apart and did the same but it was sealed pretty well with factory foam. I dried up the padding as best as I could with towels and blower but it still has a bit of water in it. I only loaded up the tools and supplies that I need for tomorrow and when I get home I am going to check it again and continue drying it out. I think this thing has been leaking since day one and the padding has just been wicking up the water and the excess would drip out the back doors. I am pretty confident that this was the problem but I have worked on leaks in houses that I was totally confident that I had fixed the leak only to find out that it did nothing. Hopefully not this time.

 

Nice sleuthing. Time will tell.

I wouldn't use silicone. I would use an auto body sealing compound, or high quality exterior window sealer (Mono, Quad etc.).

The body sealing they did at the factory is so bad. I was aghast when I stripped down my van.

 

If possible, remove the mat and get some heat & air moving on it so it can dry. If you have weeks/months of wet you are going to get a mold problem too.
Don't know if it apply to your van - my 93 suburban had a wet rear mat when I got it; dealer took it out & dried it; 2 weeks later wet again. My leak was water coming in around the driver's side tail light; water would fill the rear body panel and slosh out and soak the carpet.
Good luck - leaks are no fun.

 

Or you can throw out the padding and make a nice floor that doesn't hold on to water and dirt

 

After 2days of rain I had no water in the recessed area that was getting water in it before so it is fixed. I sent Chevrolet an email describing where my leak was coming from and the said they would send the information to the right department.