Method for manufacturing a caisson structure for an aircraft, said structure comprising a volume able to contain fuel, by the assembly of a plurality of composite parts with fibre reinforcement, characterised in that it comprises the steps of: i. producing a plurality of composite stratified elementary parts (110, 121, 122) with fibre reinforcement in an organic matrix, each part comprising a face exposed to the hydrocarbons in said caisson structure, and a zone (112, 113) forming an assembly interface for the assembly of said part without the caisson structure, the production of each elementary part comprising the steps of: a. draping plies of fibres preimpregnated with a thermosetting resin having a first baking temperature, T1, in such a way as to obtain the stratification corresponding to said part; b. depositing on the face exposed to the hydrocarbons of the stratification obtained in the step a), and without covering the assembly zone, a ply comprised of a thin film (130, 131, 132) of a polymer that is resistant to hydrocarbons and to the baking temperature T1, referred to as protective film (130, 131, 132), comprising the operations of: b.i. cutting the protective film to the desired contour; b.ii. spraying the location of the zones not covered by the protective film; b.iii. depositing the film on the stratification outside of the zones thus delimited, c. carrying out the baking under pressure at the temperature T1 of the stratified assembly obtained in the step b). i. producing a plurality of composite stratified elementary parts (110, 121, 122) with fibre reinforcement in an organic matrix, each part comprising a face exposed to the hydrocarbons in said caisson structure, and a zone (112, 113) forming an assembly interface for the assembly of said part without the caisson structure, the production of each elementary part comprising the steps of: a. draping plies of fibres preimpregnated with a thermosetting resin having a first baking temperature, T1, in such a way as to obtain the stratification corresponding to said part; b. depositing on the face exposed to the hydrocarbons of the stratification obtained in the step a), and without covering the assembly zone, a ply comprised of a thin film (130, 131, 132) of a polymer that is resistant to hydrocarbons and to the baking temperature T1, referred to as protective film (130, 131, 132), comprising the operations of: b.i. cutting the protective film to the desired contour; b.ii. spraying the location of the zones not covered by the protective film; b.iii. depositing the film on the stratification outside of the zones thus delimited, c. carrying out the baking under pressure at the temperature T1 of the stratified assembly obtained in the step b). a. draping plies of fibres preimpregnated with a thermosetting resin having a first baking temperature, T1, in such a way as to obtain the stratification corresponding to said part; b. depositing on the face exposed to the hydrocarbons of the stratification obtained in the step a), and without covering the assembly zone, a ply comprised of a thin film (130, 131, 132) of a polymer that is resistant to hydrocarbons and to the baking temperature T1, referred to as protective film (130, 131, 132), comprising the operations of: b.i. cutting the protective film to the desired contour; b.ii. spraying the location of the zones not covered by the protective film; b.iii. depositing the film on the stratification outside of the zones thus delimited, b.i. cutting the protective film to the desired contour; b.ii. spraying the location of the zones not covered by the protective film; b.iii. depositing the film on the stratification outside of the zones thus delimited, c. carrying out the baking under pressure at the temperature T1 of the stratified assembly obtained in the step b).