Only makes sense to test that front window and door for leaks
while you have everything cleared out.
Yes I said door. That little bugger can run down, hit the lip for the seat and run all the way around to the front before dripping off to the floor. Or a top seal leak can drip right onto that couch area. Don't ask how I know.
Can do a bulk hose test I would do a section at a time with that. If you get any water coming through switch to a watering can and test smaller areas until you narrow down the location to dig for.
Hinge side of door, belly band to the window, curb and street side of window, belly band around to the end of the couch/bench. Hit an area with water, then wait and give it time to work its way down before moving on to next section.
On drying out all water flows downhill so given a bit of time the moisture will all tend to end up out of there and on the floor. If you can slide a thin flexible wand up behind the wall covering any place it might speed up the process of getting moisture out. Doubt it is needed though.
You can sprinkle or blow baby powder or talc around the edge against the wall, any trace of moisture even a seepage will discolor it. Little bit of a hassle to vacuum up so I would do this only if I suspected a tiny leak that I was having trouble spotting. Focus the powder in that small area. I know you don't want to deal with cleaning up a bunch or really wet baby powder. But we used to use it to track down small oil leaks on motorcycle engines. And I have used it in the scamp
for same purpose.
Air flow and dehumidifier are probably doing the deed just fine.