The first dates have been set for the ExPats Trips to Panama : http://www.adventuretrek.com/relocation-ex-pat-treks.html
In addition to these there are several other trips that pass thru Panama, including the Trek of the Americas (goes to Argentina), and the 70 day RV Caravan with a destination of Panama City (includes briefly Mexico, and then the tourist points of Guatemala, El Salvador (coastal beach highlights), briefly Honduras, nice view of Nicaragua, thru Costa Rica, and Panama and then return north to Texas.
This info : www.adventuretrek.com
Free info to anyone wishing to do Panama overland with their vehicles.