Problem installing rivnuts into aluminum skin and steel tubing
I think that part of your problem is your use of the super economy installation tool. With that kind of tool it is difficult to hold the rivet nut very firmly into the hole.
I use this type tool for installing rivet nuts and have had good luck with its use. The tool allows you to press down firmly on the rivet nut while at the same time folding the handles together to compress the rivet nut.

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Rivet nuts are designed to allow crimping into materials in a certain range of thicknesses. They do require a hole through solid material that is a snug fit with the body of the uncompressed rivet nut. It is quite possible that you will never achieve a satisfactory result with the soft adhesive material between the outer skin and the metal tubing. One thing that you may want to try, after obtaining a better installation tool, is to heat up the area surrounding the installation site for a four or five inch area to soften the adhesive. Then with the better tool you may be able to compress the softened adhesive a bit when pressing hard down on the compression tool.