A composite storage tank may include a wall structure including at least three regions including an inner region, an outer region, and at least one permeation barrier. Another region may be optionally incorporated for venting potential permeation of fluids. The at least one permeation barrier and/or the venting layer may be strategically positioned between the inner region and the outer region to reduce or at least partially prevent fluid permeation of the inner region or the outer region. A vehicle may include such a composite storage tank. Methods of forming a composite fluid storage tank may include forming an inner composite region, applying a permeation barrier to an outer surface of the inner composite region, forming an outer composite region, and curing the inner composite region and the outer composite region with the permeation barrier to form the composite fluid storage tank.