I agree with all of the above, we have crossed several times in both directions and never had a problem. We've been boarded twice, once going into Canada and once coming home, the Canadian officer just walked through our rig and asked questions about it and traveling in a small "A" and the US officer just wanted the lime my wife paid about a buck for and declared as a valuable item. Both officers were very nice and really very sociable.
I have two additional ideas, one have a spare set of storage cabinet keys close at hand. We were asked for them once and having a set available and handing them over quickly basically ended the search for fire wood, the other has to do with sun glasses. I wear prescription glasses and have my plain set on my arm rest, I wait until the officer is looking at me and make a show of removing them so he can see my eyes and then put my other glasses on.
They really like having you prepared when you get to them. All papers readily available and a smile on your face.
