A quick stop before you leave Mexico is in Chetumal only 35 minutes from the border, a quite RV trailer park in Mexico. You can make arrangements to leave your trailer and drive to Belize for the day or longer. Your Camper will be in a secure park with 24 hour on site security.
Northern belize is not a priority destination for most visitors to Belize, even though it has so much to offer. In fact, this tendency to forego northern Belize is a very real attraction in it self...the many attractions of the north, including Mayan sites, lagoons, nature reserves and the small towns and villages are less crowded and developed than the more popular south and west.