Greif, from what I've seen, I'm sure you've got the skills to do it. You just haven't come up against something like that before so haven't worked out the methods yet.
I'm guessing that the wing thickness you have to work with is perhaps 1 or 2 mm? that's more than enough. I made slots in my 20mm Flak guns for the magazines that can't be much different in size. (you don't have mag blanks to put in them along with that barrel do you?)
The size will be so small and dark inside that you won't have to do much detail to make it look right.
First off, if you can find out what it looks like inside, great. But my guess is finding a pic of the inside of an Arado wing is next to impossible.
So, instead, find out what the inside of some other folding wings of the period look like. There's bound to be a pic of a Corsair, Dauntless or something else with the wings folded. That will give you an idea of what do do, and you can extrapolate from wheel position where the hydraulics go, and the cables for ailerons etc. should be self-evident.
Then, using a series of drills, starting from smallest to largest that will fit, drill straight into the wing until you have it hollowed out perhaps a mm or two in. Paint the inside of this slot flat black perhaps mixed with a tinge of that awful green that they use for the inside of aircraft parts (or grey if it turns out that that's what the Germans used)
Then, use a sliver of paper paper cut to shape to fit the inside of your slot in the wing, drill holes into it to represent the holes in the wing chord (frame part) and for the cables/lines to go into. You might want to make two of these paper frames for each wing, one to put as far inside as you drilled and the other to put right at the outer edge. don't worry about the paper being soft, once painted and CA's, the paper will be as stiff as if it was brass.
Use bits of wire, stretched sprue, or maybe even the ends of cat's whiskers, whatever it takes to glue little stubs in the probable position of the cables etc., with some stubs sticking out to match up with corresponding holes and stubs in the fuselage.
Now, paint as required. Keeping mind that the initial black/green/dark grey inside will give apparent depth to the construction but at the same time hide the fact that it's only a few mm deep.
The wing breaks are so small that nobody will be able to see far inside, especially past the outer frame bit of paper. Therefore, it doesn't have to be extremely detailed, since just having the suggestion of detail will make people think it's there (just like the U-boat interiors I've been seeing built on this site)
Just the hint that such detail exists in the model will make people assume such detail is everywhere.
You DID ask for help and suggestions, right?
