[LT7A]

I think the gray will make it look just right. Not too much contrast but will make it clear that you're not trying to match the truck. The texture on the camper won't match the finish on the truck no matter how bright of white you paint it. Can't tell for sure, but I'm guessing it has the simulated wood-grain stamped into the aluminum like the one I have does. With the shape and style of the windows, it won't ever really look like it is part of the truck, so it's better to differentiate it from the truck.

And just for a reference point, I think in this case the grey looks great on the wheels and will look integrated when applied to the accessory (canopy). I think red stands a strong chance of looking "applied". Probably a good (unwelcome, ha) analogy would be like lipstick. And it would wash out the features on a white truck. The sculpted bodylines would essentially "disappear" while the canopy was on it. Sorry if this is too much opinion/explanation but I enjoy digging into this kinda stuff.