Hi, I hope you get many enjoyable years out of your Montana. We also have a tiny crack as you have mentioned. However it is located on the front side just as you have described on your unit under the area of the bed. I have asked at the dealership about it and I was told that it wasn’t anything to worry about. It still lingers in the back of my mind though.
In my opinion I believe it is a result of being flexed back and forth under stress from when the landing gear has been raised or lowered during hook up to a truck. Perhaps equal pressure hasn’t been applied evenly on both jacks as the weight was shifted from the truck to the jacks, one side to the other and visa versa. It’s also located in a very small surface area where I believe the stress and flexing would have a greater impact. As I transfer weight to the truck I can see this crack open up ever so slightly. When I place the load on the landing gear I see it close back up.
This is only my thoughts and my opinion. I haven’t had the frame looked at or anything like that. The unit pulls great and it is the best towing combination I have ever had in our travels.
Take care!
