If assuming your slides are in and your trailer has the arched roof, there is no need to park it nose high. If it's a flat roof, then it won't hurt anything to keep it slightly nose high.
Personally, I'd go ahead and level and keep jacks down. Your front jacks are down all the time already, aren't they? They are no different then the rear or middle jacks.
Keeping the trailer level as possible is really best for the camper. With jacks down and level because you have multiple points of support occuring on the camper. Depending on the weather in your location, this is best for high winds and / or driving rain. The more points of contact to the ground, the more stable the trailer is. (granted, there is such a thing as too high a wind that could turn over ... even a semi-truck).
When you are parked in a campground, do you not have the trailer leveled and all jacks down? What's the difference between storage or a campground? None.
