I applaud you for taking on this little guy. You are a true hero in my book. For someone to give a dog up because they can't potty train them is beyond horrible. (just my opinion - being a dog lover and all)
It's just a patience game unfortunately. My little girl is as stubborn as they come, but she came around. Took her 6-8 months to potty train her little butt. We did the bells on the doorknob thing and it works to this day. (7 yrs later).
Have a great time on your vacation. I think it's great you are able to take them with you.