Launch iTunes and go to Store>View my account. Enter your password to continue. Look down in the section - iTunes in the Cloud. Do you see the line of type in blue - Manage Devices? Click on that and your iPad should show up in there.
If your iDevice does not show up - any re-download that you do on the iPad - like downloading an app that you have deleted from the iPad - or re-downloading a song - should associate the device with iTunes in the cloud.
Did you try downloading an app or a song that you had previously downloaded? If you delete an app - and then download it again in the purchased tab of the app store, I believe that will associate the device with your iTunes account.
Have you ever used automatic downloads on the iPad? Settings>Store>Automatic Downloads>Apps, Books>Music>On. Turn it on in iTunes as well. Launch iTunes and go to Edit>Preferences>Store> and turn on automatic downloads in there as well.
Download an app in iTunes on your computer and let it download to your iPad and then that should associate the iPad with iTunes in the cloud.
You can always turn off automatic downloads when you are done if you don't want to use it all of the time.
That is the challenge...I have done the above Store>Account>iTunes in the Cloud>Manage Devices...but my iPad is not on the list of Managed Devices. How do I add it to the Apple ID acount??
I wouldn't worry about it. This only applies to items set for automatic downloads.
If you want it to show up then enable automatic downloads in Settings > Store.
I have an iPad and two iPhones with one AppleID and everything works fine.
Only the iPad shows up in Managed devices (because it is the only one I have enable automatic downloads for)