I've been traveling in Mexico in a 37' with just me and my wife and haven't regretted trading in my 32' one bit! The added length hasn't been that big of a problem, primarily because I also tow a Toyota Tacoma pick-up with a camper shell. If the place I want to go isn't conducive to big rigs, I just go with the Taco and either use hotels or a tent (with an air mattress, of course). But that hasn't happened very often. From the Tip of Baja to the tip of the Yucatan, and all places in-between we've always been able to find a place to park the coach within day-trip distance of anywhere we wanted to go.
That said, I've also lost mirrors on the highway and have had most of a town's population and cops turn-out to help me back out of their town square too! The locals and the cops were always gracious and pleasant. Apparently they think Gringos are funny and like to watch them step on their own reproductive organs.
It's all part of the experience!
But with a family of 5, you might want to check out a toy box with an aft bunk room. 5er are easier to handle because they bend in the middle, or so I've been told.
