Welcome to FGRV Irene,
Phone Tom at the # listed on the parts order page
It is the 16' Doorway bulb seal for $54.
He is in Ontario right now. His cell coverage is sporadic up here, but he gets messages if you leave them. He is handling the orders until July 30 after that it appears the parts are going to be handled by Great West Vans
Parts | Trillium RV
If it helps, I'm expecting him to drop by my place near the airport one last time before he heads back to the USA. He did have some parts with him. I'm not sure what he has or has left on this trip.