A modular fuel cell stack assembly (1, 100) comprising: a plurality of fuel cell stacks (2, 102, 402), each of said fuel cell stacks having a plurality of stack faces (61, 62, 63) and a plurality of stack corners formed between said stack faces, wherein said plurality of stack faces (61, 62, 63) include a cathode inlet face (102a1, 102b1, 402a1, 402b1, 402c1, 402d1) adapted to receive oxidant gas for use in a cathode side of said fuel cell stack, a cathode outlet face (102a3, 102b3, 402a3, 403a3, 402b3, 403b3, 402c3, 403c3, 402d3, 403d3) adapted to output cathode exhaust from said cathode side, an anode inlet face (102a2, 102b2, 402a2, 402b2, 402c2, 402d2) adapted to receive fuel for use in an anode side of said fuel cell stack and an anode outlet face (102a4, 102b4, 402a4, 402b4, 402c4, 402d4) adapted to output anode exhaust from said anode side, and wherein at least one of said cathode inlet face (102a1, 102b1, 402a1, 402b1, 402c1, 402d1), cathode outlet face (102a3, 102b3, 402a3, 403a3, 402b3, 403b3, 402c3, 403c3, 402d3, 403d3), anode inlet face (102a2, 102b2, 402a2, 402b2, 402c2, 402d2) and anode outlet face (102a4, 102b4, 402a4, 402b4, 402c4, 402d4) is an open face without a manifold; a containment structure (10, 110, 210, 310, 410) for housing and enclosing said plurality of fuel cell stacks (2, 102, 402) and for providing fuel and oxidant gas to said fuel cell stacks; and a sealing assembly (107, 407) forming at least one sealed chamber (108a-g, 408a-k) for sealingly enclosing and isolating at least one said open face within said containment structure (10, 110, 210, 310, 410), characterized in that said sealing assembly (107, 407) comprises a plurality of seals (107a-h, 407a-n), each of said seals including a seal press assembly (109a, 209a, 309a, 409a) adapted to be applied to a stack corner adjacent said at least one said open face, a spring member (109c, 209c, 309c, 409c) for providing a force so as to retain said seal press assembly (109a, 209a, 309a, 409a) at said stack corner and at least one separating member sealingly coupled with said seal press assembly (109a, 209a, 309a, 409a). a plurality of fuel cell stacks (2, 102, 402), each of said fuel cell stacks having a plurality of stack faces (61, 62, 63) and a plurality of stack corners formed between said stack faces, wherein said plurality of stack faces (61, 62, 63) include a cathode inlet face (102a1, 102b1, 402a1, 402b1, 402c1, 402d1) adapted to receive oxidant gas for use in a cathode side of said fuel cell stack, a cathode outlet face (102a3, 102b3, 402a3, 403a3, 402b3, 403b3, 402c3, 403c3, 402d3, 403d3) adapted to output cathode exhaust from said cathode side, an anode inlet face (102a2, 102b2, 402a2, 402b2, 402c2, 402d2) adapted to receive fuel for use in an anode side of said fuel cell stack and an anode outlet face (102a4, 102b4, 402a4, 402b4, 402c4, 402d4) adapted to output anode exhaust from said anode side, and wherein at least one of said cathode inlet face (102a1, 102b1, 402a1, 402b1, 402c1, 402d1), cathode outlet face (102a3, 102b3, 402a3, 403a3, 402b3, 403b3, 402c3, 403c3, 402d3, 403d3), anode inlet face (102a2, 102b2, 402a2, 402b2, 402c2, 402d2) and anode outlet face (102a4, 102b4, 402a4, 402b4, 402c4, 402d4) is an open face without a manifold; a containment structure (10, 110, 210, 310, 410) for housing and enclosing said plurality of fuel cell stacks (2, 102, 402) and for providing fuel and oxidant gas to said fuel cell stacks; and a sealing assembly (107, 407) forming at least one sealed chamber (108a-g, 408a-k) for sealingly enclosing and isolating at least one said open face within said containment structure (10, 110, 210, 310, 410), characterized in that said sealing assembly (107, 407) comprises a plurality of seals (107a-h, 407a-n), each of said seals including a seal press assembly (109a, 209a, 309a, 409a) adapted to be applied to a stack corner adjacent said at least one said open face, a spring member (109c, 209c, 309c, 409c) for providing a force so as to retain said seal press assembly (109a, 209a, 309a, 409a) at said stack corner and at least one separating member sealingly coupled with said seal press assembly (109a, 209a, 309a, 409a).