I have no adrenals (which is the same as having non-functional adrenals, except, well, I have no options, I don't have any fallback but meds where your adrenals may produce some) and I have MG. I had Cushing's disease before (too much cortisol - like taking too much pred) and had to have them removed or I was going to die - and oh yeah, you cannot live without your adrenals so you have to be careful. You need to find not just any endocrinologist, but one that knows what they are doing. Not all of them know how to test, or how to treat. Too much is as bad as too little (hence why those on lots of pred get Cushingoid).
I have a lovely tan (hah) too.
ACTH is the cause. It is a very fussy test - you must get the tech to do it right, or the ACTH will degrade and your results will be lower than you are. It has to be spun and frozen promptly - minutes, even seconds count - I get 800+ point variations in mine and the range is only 5-27 so you can imagine it is hard to get an accurate test if your tech is an idiot (combined with an endummy), you will get no where.

This is good reading too:
http://www.addisons.org.uk/info/manual/page1.html
Make sure you have extra steroids, take them properly, and have an emergency kit. Stress dosing when you are sick is also necessary - you basically have to do with pills what your body would but cannot do naturally and guessing - and you have to do it accurately. Get a medic alert bracelet too.

Let me know if you have questions - there is a lot to this.