It’s possible to drive the entire length of the Interamericana (often referred to as the Pan-American Highway outside of Central America) from North America to Panama [1], but this is a long, serious trek and there’s always some risk of encountering bandits, brutal roads, and dyspeptic border guards.
Making the trip requires serious planning and a well-equipped vehicle. Allow about three weeks from the Mexican border to Panama at a reasonable pace. Bear in mind that North American auto insurance policies don’t apply south of the border.
Cars rented in Costa Rica [2] cannot be driven in Panama, and vice versa. Even trying to drive cars registered in one of the countries across the border into the other is a nuisance and a source of continuing squabbles. It’s not worth the hassle for a short trip; take the bus instead.
RV convoys occasionally make pilgrimages down the Interamericana. The only true RV park in Panama is XS Memories (tel. 993-3096, fax 993-3069, www.xsmemories.com [3]) in Santa Clara, about a two-hour drive west of Panama City [4]. It has 22 hookups for campers and mobile homes and can provide current information for those interested in shipping vehicles to South America.
Links:
[1] http://www.moon.com/destinations/panama
[2] http://www.moon.com/destinations/costa-rica
[3] http://www.xsmemories.com
[4] http://www.moon.com/destinations/panama/panama-city