First, congrats on the new RV.
Second, that leveler is the good one - the fully automatic leveler and the one I have on my 3051s. Works great.
Second, that gap in the rear exit window - or more appropriately the misalignment of the window in the opening is something I have too. Mine almost fits the weather stripping gasket - but not quite on the right side. There is also a 1" opening in the window frame below the window. I guess to let condensation drain out - but it really lets cold/hot air enter directly to the inside of the RV.
Plus that huge window is single pane and thin as can be. It's a huge cold/hot spot at the back of the RV. Frankly, unless the weather is perfect we keep a piece of that reflective covered bubble-wrap insulation in that back window all the time. It keeps the Sun from baking the bedroom during the day and the cold from freezing the bedroom all night.
The window is supplied by Cleer Vision and I'm looking at replacing the whole thing with a double pane window with an opening emergency exit that has a screen. https://www.cleervision.com/
All of the windows are sabotaging the heating/cooling of the RV. I don't know what it would cost to replace them with dual pane windows. But I plan to check this out.