Hi lowbridge,
Welcome to the Heartland Owners Forum and Family. We have a great bunch of people here with lots of information and all willing to share their knowledge if needed.
I would suggest you drop the front part of the cover from the frame. That way you can see what is there and also find the location of the floor joists. Not hard, just a few screws and then you can be sure. You really need to remove it any way to put nuts on the bolts. At least I used bolts and nuts,,, not wood or metal screws.
Enjoy the forum.
Jim M