Have your travel documents in your hand or the hands of the person in the passengers seat. The DW has a folder that is well organized and has trip info, passports,insurance papers and pet's papers are in my hands. I don't know about now but the pets papers had to include a statement regarding being in good health and vaccinations. Our Vet had a form he filled out.
If you have a long gun or sport shooting handgun with you, you should have the proper forms issued by their customs office indicating why you have a gun and if the gun is locked up someplace have the key as well.
No sunglasses on anyone in the RV. Best to let the BG see that you're were wearing and removing before approaching the station. Look at the BG's face, your eyes tell them a lot.
Answer quietly and quickly, usually a yes, no, USA type response. Always be truthful and don't joke or volunteer info. Don't answer for others who are asked questions.
Those guys are just working stiffs with a thankless job. And if you are forthright and respond quickly their job is easier and theu appreciate your help.
You should be just as respectful to our BGs and have all the papers you need to cross back into the country ready for them too.