Acid etching an Airstream exterior, in preparation for a primer, "is not a good idea."
No amount of work, even steam cleaning the metal after etching, will completely remove all the acid.
That being the case, the acid in time, especially around the rivet heads, will "eat through" the paint. Takes a while to do it, but it will happen.
A much safer, far superior but tougher way to prep the surface, is to sand it with 120 to 150 grit sandpaper. Do not sand any of the rivet heads, until the rest of the trailer has been sanded. Then, and very carefully, lightly sand the rivet heads.
Deglossing, or scuffing won't get it. "Sanding where the original finish is absolutely gone," is the method that must be used.
This provides a surface that the primer will bond to extremely well.
When done properly, the paint will never chip, even from hail.
We have a motor home door that is absolutey crushed, yet the paint did not crack, chip or peel away.
Of course, the quality of the paint materials must be "first class."
Using this method, as we have for 40 years, totally and safely, avoids the acid issue.