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I have designed a removable horizontal stabilizer which slides over the vertical stabilizer, your part CE3_fusoliera_detach_part1.stl. I find it to be much more robust than your magnets. There is a small hole in the top for locking it into the vertical stab with a small screw. You are welcome to add this to your thing files for this plane. I find the part prints well standing on the trailing edge, with a 10 row brim. If you leave the brim in the center section on the bottom, it makes a nice stop when sliding the horizontal stabilizer onto the vertical.
I have attached a couple of photos, as well as the .stl and .scad files.
I am in the process of building two planes, and plan on flying them in the 3rd week of May, on a trip to Kansas. I will give a report when I return.