In creative, scouting seed. First portal seen generated under water. 

Replaced missing pieces and crying obsidian, then used sand to surround it and create an air pocket within the frame. Each pre-existing piece of obsidian let water through like it wasn't there. Had to replace each one before portal would be dry enough to light.

Seed:   -718530799, co-ords in screenshots. There was no visual difference I could see.