I concur with Vance, Carsten and Peter ..., a single o-ring witht the correct hardness is the way to go. See technical note
http://www.satoriseal.com/Technical/introduction_to_o-rings.htm on how o-ring is design to move within it's machined grove under pressure to seal. Hatch upper and lower faces need land face to face. If you are designing a hatch, pick a standard size so that you do not have to introduce a splice.
Great works are performed not by strength but by perseverance.