This question has been asked ever since slide outs were invented. From my experience, there are two important factors to consider when deciding which option is best for your RV storage.
In my opinion, it is better to store your camper with the slide in. Your RV’s slide is designed to be out and can be out as long as you want, which is great when you’re camping for extended periods of time. But having the slide out also changes your camper’s center of mass moving it closer to the exterior wall, which can add a little of stress to the frame. And unless you’ve built on some solid skirting and have a slide topper, then keeping your slide out gives easier access for water and bugs to get into your camper. I recommend storing your camper with the slide in.
If for some reason you really want to store your camper with the slide out, there are some things you can do to reduce the risk of something bad happening.
Support the slide’s weight when it’s out
I once knew an older gentleman camper who was over 6 foot 5 and weighed about 250 pounds. His camper had a slide out that was at least 15 feet long and held a big hide-a-bed couch. For safety reasons he made two metal stands that were the perfect height for the slide out the rest on when he was parked on level ground.
The manufacturer didn’t say he should do it. He was just concerned about his added weight on the couch when the slide was out could make the trailer a little tippy.
All that to say, if you’re concerned about the slide being out during storage adding a little stress to the frame and throwing off the weight distribution of your RV, then you could do something similar let
Store under a cover or with a really good slide topper
If you’re storing your camper out in the open with the slide out then there’s a chance that water will accumulate on top of the slide out. And potentially find its’ way into your camper at the joints.
This is especially true if there is a lot of wind in your area and small puddles of water on top of the slide out are blown into the joints.
Storing your camper under a cover so it’s completely safe from rain and snow solves this problem. If a cover like that is out not in the budget then a good slide topper will prevent water accumulation.
If a good slide topper is not in the budget you could duct tape a tarp around all the sides of the slide so that all the connections to the main RV are covered by the tarp.
But if you’re going to go through all that effort, why not just pull the slide in for storage?
Protect the bottom connection of the slide out
Now that you’ve protected the top of the slide out from what accumulation, you have to protect the bottom from bugs.
If you go under your slide when it’s out and investigate where it connects to your RV. You’ll find there’s a small gap between the slide and the main RV. Over time small bugs will find that gap and crawl into your camper.
You might think the gap is too small for any bugs to get through, but you would be amazed. Get this, according to the Terminix website, mice can squeeze through a crack or a hole that is as small as the width of a regular pencil (or a quarter inch or six millimeters).
If your camper’s slide has been used a good number of times I’m willing to bet that you can find gaps that small somewhere in the slide connections to the main RV.
I know what you’re thinking, that gap is a few feet of the ground, a mouse couldn’t possibly get to it. You’d be amazed again.
And remember, the main point was that small bugs would get it and they can crawl upside down under your RV, the up the side and into the gap.