I would not use enough of any liquid as to cause droplets. Then I would also not reach into the chassis. You can reach inside the cabient but not within the cofines of the chassis itself. The caps in there will kill you dead. It is a one time deal, death. It is officially game over and you have no more quarters. Got it?
If you want to completely erradicate stuff like rust you should just replace components that are rusting. It is difficult to save anything that has already begun to corrode. Some light surface rust can be removed via steel wool or similar but I wouldn't want to use it near my amp because it will create tiny broken metal threads to be exposed to your amp as well as the now corroding dust that is created by physically removing the corrosion. In addition to this the light particles and broken steel threads can be attracted to your speaker's magnets or any other polarized part of your amp. If you do take the physical removal path then be sure to prime any exposed metal with something to keep the metal from again corroding. It is important to completely remove the corrosion though before you do this, then clean it with alcohol or similar to remove any oils, and immediately prime the affected area. It is simpler just to replace rusting parts. By the time you get everything you need to restore it and do it you could have saved a lot of time and money by just replacing parts because you might not erradicate the corrosion even though you did your best and tried real hard.