Sounds like a great trip - I am EXTREMELY jealous.
Suggestions:
1) Dont bring too much gear - less is more in Central America. You make yourself a target by showing off your "stuff". I have been guilty of this but over time learned to trravel with a daypack, a sheet, and two changes of clothes and some basic food items like canned tuna and sardines.
2) Make sure you park the truck and get out on foot and take a few buses. The culture is rich and your not going to expereicne it very well from behind a window.
3) Don't just hang out with others like you, be outgoing and meet some locals. Getting out of the truck will help you accomplish this. Instead of staying at a hostel or hotel, ask around in town for a place to stay - store owners or clerks are a good place to ask. Someones backyard is a great option when you get to meet their family and friends too.
4)If you dont speak spanish, learn, or focus the trip on Beleize where they speak a dialect of english (Beleize was a British colony untill 1981 when it gained solidarity).
5)You dont need a heavily modified vehicle to get around and get into the backcountry - during my 3 years in the Peace Corps in Panama all we had were state department 80 series and 100 series cruisers and they were stock with MTs. They got stuck sometimes but that is part of it. Hardly any of the locals have modified vehicles and they can get into most places where the dirt tracks go.
6) Watch out for malaria, botflies, aemeboic dissentary, etc..... May want to bring some cloroquine with you to take to avoid Malaria. We saw lots of Malaria in Panama while we were there, Beleize has a history of it too.
7) Dont worry too much about safety and security. It is what it is. In my time down there I only have three really bad experiences which are paert of the adventure. I have only been robbed once. With the police, just make sure you smile and stay up-beat, dont argue but dont agree. I had diplomatic immunity in Panama so cant speak to that there, they simple let you go after showing them your "Funcion Administrativa" ID card from the State Department. Haha.
8) If you go to Beleize, I strongly suggest reading this book to get an idea of what the Country is all about, problems it has overcome, and the cultures within: The Making of Belize: Globalization in the Margins by Anne Sutherland.
As a qualifier I have spent several years in Panama, almost a year in Beleize, and several months in Costa Rica between 1999-2003.
Enjoy. You are NOT going to want to come back.
