OSM + Garmin for cycle touring South America

I appreciate any help that you can provide a person new to OSM and not very tech savvy.

I am currently deciding between using paper maps or buying a Garmin 62S for a bicycle tour of South America beginning in Colombia. There will be huge advantages with the Garmin, but I’m trying to figure out the feasibility of it. I understand that I would be able to download OSM maps for the countries I need to an SD card before I leave, and then use the cards in the GPS. However, I do not plan to have a laptop with me and I will not have the trip exactly mapped out before I leave. Would I be able to use the maps and GPS to program my route from the GPS as I go, or is it necessary to do it using Basecamp software (or alternative) from a computer?

Any other comments or insights from anybody who has used OSM street maps in South America?

Thanks in advance

A question like yours was asked on the Dutch world cyclists forum (use google to translate) http://www.wereldfietser.nl/phpbb/viewtopic.php?f=21&t=18794
In general you can plan routes on your gps so you wont need Basecamp for this. A computer or smartphone could be handy to plan your trip because not all roads are on OSM in South America but you can find internet places everywhere I guess. There are also other free alternative maps see http://www.gpsfiledepot.com/maps/