Welcome and congrats on your new Montana! I hope it serves you well.
Considering you have one camper under your belt now and experienced multiple problems with it, start right now doing some pre-preventative maintenance on your new Montana before maintenance or repairs are essential.
For example ... you know there are drafts caused by holes in the underbelly of the camper. And you know those drafts blow up through the grate in the steps leading to the upper floor level. So, take the time right off the bat and begin sealing up all those holes and gaps. This will improve your furnace efficiency, your air conditioner efficiency, and eliminate drafts on the lower floor.
Take the time right now to add a sealers, calkings, glues, nails and screws around trim pieces, check the supports in your kitchen and dresser drawers and strengthen them now before they fail bouncing down the road. Reinforce the closet clothes bar to eliminate future bending or it even coming off the wall or the shelf it's supported by from collapsing. Go around the outside of the camper and UNDER the camper right now and make sure all the screws are tight. You'll be shocked how many actually are not in anything solid. Take the time right now to make sure your wheel fenders (those plastic things) are attached well, and stop the screw holes from cracking out before they even start.
You know the vunerabalities, you experienced all once before. So, work ahead of the game, remember all those things that went wrong with your previous camper and check those items on the new one, make new supports, fixes, or whatever to ensure the same problems won't happen again.
Contrary to all best intentions, the first year of ownership will unearth stuff that needs repair. If you jump ahead right now and address the known issues that happened to your last camper, you have a better chance at a good success rate with your new camper.
I wish you all the best in the world. And I certainly hope your issues are nill!