I have opened the slides while hooked to the truck with three different Fifth-wheels. No problems. If your slides bind while being hooked up than your frame is broken or not designed correctly. Yes I also in manual mode level out the Montana (with in reason) for short time (lunch etc) or overnight. I have never been to an RV dealership or RV Show either where all the units were all leveled up on all the jacks and yes every one had all the slides open. Have a safe trip and enjoy your RV.
Happy and safe roads to you.
Tom Marty
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