Jerry - If you leave the jacks down and heavily loaded for long periods of time there will be a certain amount of internal leakage and the jacks will retract some. In general, most hydraulic systems I a familiar with are left in a store position with pressures released, or at least not heavily loaded. That being said, the slides retracted are loaded so if you want to go by the same rules, you should also release the slide pressure also. Personally, I would leave the jacks up, not because of internal effects of pressure but because it keeps the shaft protected from the environment since it is no longer exposed when retracted. Long exposure to the environment will cause corrosion and pitting, resulting in leaking jacks or even worse.
'01 Alpine 36 FDDS