In my experience, it's been a mixed bag.
I crossed at Sweetgrass once, and had the experience you describe. EVERYTHING emptied out of the rv while I sat in a waiting room, they took the keys to my car and trailer, this was by the Canadian authorities. After the RV was empty, they called me out and had me remove my dog from the car so they could give it a thorough going over. At least they were nice enough to put most everything back away.
I don't recall where I returned to the US on that trip, it might have been Portal ND.
A year later, I crossed (again?) at Portal ND, which was a busy freight port of entry. Other than filling out paperwork for a long gun, the process went super smooth. No inspection of the RV or car.
Crossing from Canada <> Alaska was no issue either way multiple times.
Crossed from Canada to US at Roosville MT (tiny like Sweetgrass), they put up a bit of a stink because I didn't "optionally" register my long gun with them before leaving the US. I was able to provide them the receipt showing I purchased it in the US (and no duty was due) and was on my way. No searching or extensive questioning.
2013 KZ Sportsmen Classic 200, 20 ft TT
2020 RAM 1500, 5.7 4x4, 8 speed