I speak from first-hand experience. As part of the BeetleBall 24 'rally', I've crossed into Canada, back into the US, and into Mexico in 2009 and again in 2010, with a modded 1965 VW Bus. It was outfitted with a front airdam and side shirts, then water injection pumps, hoses, water cooler. And it had sponsor stickers up one side and down the other.
Canada: on one of the trips, we crossed at 2am. Not a good plan when you stand out like a sore thumb, like we did. The border guards are on their toes most of the time, at 2am they have plenty of time on their hands. They asked us to pull over and go inside to talk with the agents, splitting up my buddy and I. They asked all sorts of questions pertaining to our stay, personal stuff that they could verify through (likely) the interpol and other databases they seemed to be searching. Then the questions about the VW. The guy seemed to know cars, he understood when I volunteered the details of my water-spray-cooling and water injection systems, the water cooler with wires and hoses hanging about in an improvised manner. On another trip, my buddy Greg, who is Hispanic, was ordered to "turn off your vehicle and hand me the keys". The questions came, he asked me a series of questions, then let us go. We got the same treatment coming back into the US from Mexico. After those 2 experiences, we made sure my Caucasian-ass was behind the wheel for all future border crossings. Neither my Hispanic buddy Greg, nor I, are the least bit bothered by the profiling, 'it just is what it is' we both agreed. I minor inconvenience.
Mexico: Again, about 3am, crossing at El Centro/Tijuana. The Mexican border guards eyed not only the plumbing and wires, but all the tools we had strewn about after making a roadside repair around 10pm. My gal, wearing a dress while strapped into her seat with a red 5 point racing harness, also looked out of place. After pulling into one of the stalls, they converged and talked in Spanish, which I couldn't understand. One guy asked me, in broken English, to open up the back. Looking at the mess of parts, wires, cooler, and assorted gear "what's all this... STUFF about". The old air-cooled VW's are still very popular in Mexico, "It's spare parts and tools to keep this thing running" I said, showing my greasey hands "we just fixed it... AGAIN". He gave me the universal nod, shrug, and smile that mechanical guys give each other, when we feel the other guys pain. He paused, rattled off something to the other guys, nodding, then said "ok, you can go".
One other thing. We were using off-road racing noise canceling intercom headsets to communicate. At 90-100mph, that stripped down VW '65 Bus (hot-rod 2liter engine with free-flowing header and muffler) was LOUD! We were also using a flip camera to record some of the trip. Before coming to the crossings, we put all that stuff away. No sense raising more questions.
Looking back I'd say be prepared, they WILL ask, they are trained to look for anything out of the ordinary. A blue-haired grandma driving a 911 turbo, a 7foot basketball player driving a Fiat 500, a young kid driving a Buick Delta 88, any modified car driven by anyone.
