Videos from iTunes to iPad disappear, only iCloud download

The problem that I am having is that after I have synced TV episodes that I have purchased and downloaded from iTunes to my iPad, the episodes later are not on the iPad, and instead require downloading from the cloud again to watch. This is a problem when I am traveling outside the US. I have tried all I can think of: While connected to iTunes, deleting the episodes and then resyncing them. The episodes are on my iPad, ready to go. Then a few days later, when I'm on a plane or overseas, the episodes aren't there, requiring download again from the cloud, which isn't possible in these locations. I have even tried to copy these episodes into another iPad app to view them, but the restrictions on the iTunes videos means they aren't viewable even though they are on the iPad. Why are the episodes removing themselves from my iPad, and how can I keep them there and available? Thanks!