When your slides are in, the rubber seals are covered up and better protected from the weather, plus it should form a tight seal on all edges of the slide when closed.
Below are a few reasons why I would close them...
- Rain water can pool-up and run into your coach from the seals if the coach (or slide) is not level.
- Inspect every seal on each slide to make sure there are no gaps, openings, loose or poor fittings.
- Open slides will give bugs a better chance to find a way inside your coach around the seals.
- With your slides open, the rubber seals are more exposed to weather (hot sun, rain, dirt, etc.) which can in time dry them out to where they will crack and/or deteriorate. Apply slide seal conditioner minimum 2x/year to keep the rubber soft.
- You also expose much more surface areas of your coach to the weather when slides are open.
- Nothing will be noticeable right away, but over time you will start to see your seals become more worn, the roof of your slides will be grimy from being left open all the time.
- You never know what kind of weather conditions will occur when you are away, and weather can be one of the hardest things on an RV.
- As previously mentioned, less space to heat and cool when slides are in.
- Final note... make sure to get wheel covers for your tires to protect the rubber and rims.
Hope this helps...