I originally designed it to slide into place and be held by air pressure and magnets.  There is a central screw, that on the last attempt, I added a larger diameter washer too to make sure it held to the scoop and the screw was glued in to prevent screw loss.  On my last flight of the winter season, it fell off as I was on the final turn for a low high speed pass.  The pictures below should help explain how the scoop was connected and I will show what I have done to solve the problem.

At the back you can see two holes for dowel peg aligners and the rear magnets.  In the center of the wing is the screw that holds the front of the scoop on.

Here is the slot that the center screw on the wing slides into.  

For the fix you can see in this photo that I have carved out the foam filler, added a 1/8" piece of aircraft ply, and a straw.  The added ply layer acts as a washer for a machine screw and the straw as a guide.

Here is where the straw comes out on the bottom of the scoop and I have filled in the bobo with some Evercoat body filler.

Here is the scoop in place and the straw exit area cleaned up and painted.  I don't have a picture of it, but after the matt clearcoat, it blends in perfectly.

At the point where the machine screw meets the wing.  I cut into the wing and inserted a 1/2" diameter dowel straddling the F1 wing formers.  Then I drilled and tapped the dowel for a long 4-40 machine screw.  This should now take care of this problem.

Now the P-51 is ready for the flying season...oh, but wait .  

While trying to cycle my NiMH battery packs, I kept getting an error on one of them.  I'm running dual batteries as a redundancy system, and this is a perfect example of why.  Long story short, I ordered a new battery to replace the one.  Then after an autopsy I had one bad cell in the five cell pack.  I also discovered that my wire ties holding the batteries in appeared to be damaging the outer wrap of the battery and possibly the negative wire underneath.  I went back and added some more battery foam wrapping along with protective electric tape over that before wire tying them back in with a little less overall pressure.  Now, I'm ready for flying season!