Contrary to what HWH writes, in my opinion (based on over 4 decades of experience with hydraulic systems):
A cylinder's extended actuator rods:
1. are not able to resist long-term exposure to the elements and will rust.
2. will collect dust and dirt.
Then, aside from damaging the surface of the rod, retracting and extending the dirty/rusted rods will eventually damage the cylinder seals.
Therefore, unless you're able to regularly clean and lube the rods (with transmission fluid), best to keep them retracted during storage.
Also keep this in mind when parking the rig for extended periods; regardless of chassis, turn the steering wheel in whatever direction that will most completely retract/house the steering damper's rod.
Last item: although initially protecting the cylinder rods, those neat accordian type covers on some aftermarket dampers will eventually break down and allow moisture and dirt to enter and be trapped, resulting in damage as described in items 1 and 2 above.