It appears as though Southco is the supplier for compartment door gaskets. The cross sections can be viewed here:
http://www.southco.com/resources/documents/GA.en.pdf
Their main gasket page & contact information can be found at
http://www.southco.com/class/ga-gaskets-7580.html
I would guess that you could contact their distributor in Elkart,
http://www.southco.com/contact/conta...on.aspx?lid=15 to find which gaskets are supplied to GulfStream & if they could provide you with the length you need.
Sorry I couldn't provide the exact part number. I'm assuming this is the gasket you're asking about?