Hi John,
Border crossing in South America is absolutely no problem. I traveled 18 months in South America. I started in Caracas, Venezuela and flew back home from Buenos Aires, Argentina.
I have some more information about
border crossing in South America. You'll see that it is very straightforward.
Don't hesitate to post more questions if something is still bugging you. I'll do my best to help you out.
Best wishes,
Mark