That is identical to the fill door on my 2007 Access 29T.
The seal is supposed to be that sponge neoprene but it has never sealed well.
Take a corner too fast with a full tank and you'll see the water droplets running down the side of the rig

I would just buy some more off Amazon. You can buy it in white with the sticky back.
Just search for "White Neoprene Sponge Foam Rubber" and I'm sure you'll end up with enough to send me some.
Cheers