We spent some time in Belize in the smaller towns in the northern part. We had no issues with crime but were vigilant and careful.
Then, we travelled north into Mexico (something very few Americans can say). It was another world. Machine gun armed roadside stops to "fumigate the vehicle for pests" - along with the bribes to go with that. Difficult border crossings and money exchanges. While we did OK, we were definitely marks for everyone around us.
If I could somehow get the RV to Belize, I would love to do it. But I would never travel through Mexico to get there.