The funny thing about cats is their dependency on humans is absolutely zero. They don't NEED you for food, fun, warmth or comfort; you may think they do, but they really don't. Any cat is just over a month away from going feral. Cats are territorial and are much more comfortable having their own territory; as soon as you move them out of theirs, they are scared and concerned they're infringing on another cats territory. It messes them up.
So that being said, cats really hate to travel, period. They would much prefer you leaving a huge bowl of goodies and water somewhere safe and will be just fine until you return. A cat door allowing them access into your home for safety is good but not necessary. You can also get collars that emit a signal to the cat door that will siganl the door that it is the rightfull owner wanting to pass, and not you local raccoon.
I know this is not what you wanted to hear, but hey, it's MHO.
Cheers
Tony