Most RV's require the slide be opened all the way to prevent wind from blowing in rain, or dust, as there is a interior slide seal that only engages while open 100%.
I have never seen a slide out that you just push one button and all the slides either retract or go out. I would think that to be silly design, as you might be in a situation that you can only slide out one into the street or something, or one slide might be next to the power post, tree or something else and must be left in for that trip. .
Some carry a cut off broom stick, that is 3' or 4' long (depending on slide length) and use that to make sure the trailer is in the correct position before opening the slides and before disconnecting the truck and making it level.
Newer slide outs, you can safely sit in them while they go in and out.
I would go back to that dealership, ask the salesperson (if they still work there) to slide out one, and part way. Look for sunlight between the sides of the slide. See if dust will blow in.
I think he is blowing smoke that they can be left 1/2 way out and no rain will get in. Sure it is possible, but most slides that I have seen might leak in some rain water.. . .
Fred.
