I can usually preface my questions by saying this is probably a dumb question. I want to reinstall the rear end back on my 1 ton truck. I am thinking if I put the new brake cylinder and shoes on, I will be compressing the brake cylinder. Since this truck is sitting outside, it may be years before I ever use the new brakes. I am thinking if they sit unused outside, everything is going to get rusty or ruined from having them sit. I do have a new master cylinder, but I would need to attach the bell housing which is still attached to the motor inside of my shop. I would need to remove the transmission, clutch and flywheel, and prep and paint the bell housing. Doable, but I am not sure filling the cylinder with brake fluid is going to solve anything, except I could press on the brakes once in a while to keep the parts moving.
So don't put them on until it's close to when you will use them. Store them inside where it's dry and cool, may not hurt to use a baggy with a rag soaked in oil to wrap them in until use.