My Enstrom lives outside with a cover on. The cover is breathable but it is often wet with condensation inside. Corrosion on the tailcone used to be a problem and it has had to have the paint touched up.
A few years ago I started to use Lear ACF50 inside the tailcone (and everywhere else) . It is 'misted' using a fine spraygun so it penetrates everywhere. It works by neutralising the corrosion cell. It has solved the problem.
It is expensive at around £100 for 4 litres but this will last for ages. Fantastic stuff. Doesn't seem to harm anything and protects everything.
Just a very satisfied customer.
Check with your engineer before applying to your aircraft.
PS I do mine 4 times a year. It takes about 50cc and 10 minutes to do the whole aircraft. Wear a mask. Its bloody awful if you breathe the spray.
PPS The aircraft is 32 years old and was last painted in 1988.