Travel with Pets - Potty tips/advice for in-cabin international flight?

Hey there. I'm going to be flying JFK-TXL (Berlin) with my 15lb rat terrier in about a month. She's very, very good at holding it when she needs to, but I'm wondering what experiences others have had with the potty situation. Just thinking about sitting at the airport for a while, then on the flight, then dealing with customs... it's going to be a LONG time before she can go outside. Should I start trying to wee-wee pad train her now, so I can give her opportunities when it's reasonable?

Thanks in advance for any advice, stories, experiences, etc.!