91lux
The easiest and surest way I can think of is to place the IP in a container and submerge it in a light weight oil. Cover and store. You can then forget the IP until you need it.
I would stay away from diesel fuel or any other similar liquid. Diesel and similar liquids do strange things to the gaskets on the IP. You may consider removing the solenoid(s) and storing them separately. I do not think oil would hurt the solenoid(s) but it is better to be safe than sorry. Also, be sure to plug the coolant passages before you add the oil, if you choose to use this solution.
Good luck
Iverson