Traveling to San Carlos

We are thinking about traveling to San Carlos Sonora next month and have some questions. We talked to the gentleman in the big tent at Q and he mentioned that we should park on the US side and walk over to get our paperwork in order and then come back and proceed with the RVs. Other people say that there is no paper work at the border and we do everything at km21 check point. Apparently we do not need a TIP for the truck but how about the fifth wheel trailer. People traveling with us have a motorhome with toad. Do they need a TIP. Insurance-- We know we need it. Can we buy it online and if we do, where do we get this sticker or is it better to buy it at the border? Any recomendations? We were told to take the truck lane around Nogales and can we buy this ins there? We are excited and nervous at the same time as we are rookies for traveling in Mexico but we are really looking forward to it. We are Canadian if that makes any difference.

D&H