Zandy,
I am like you in that I don't experience ear problems except on planes. I had one very bad experience flying to Bermuda, when my ear didn't pop for 6 hours and I was literally in tears in my hotel room with the pain. (I tried everything to help to no avail) When preparing for our first trip to WDW, I read on the boards that a low dose of decongestant can prevent problems. So about an hour before we boarded, my children and I took a dose of chewable children's sinus medicine, and it did the trick-no problems. (It did make them sleepy, which isn't a bad thing on long flight). I also brought a saline nasal drip stuff I had read will help clear sinuses if you do have problems, but didn't have to use it. I will always take this precaution for future travel.
Kathy