Albert:
Interesting route plan and questions. I'll address only the Pan American through South America as that is what you specifically asked about in the title of your thread.
Three times I've done Colombia to Chile, and then over to "Fireland", twice on different 1983 Honda GL650s, and once (1997) on a well worn 1981 BMW G/S, so not a Harley-Davidson but tired and old motorcycles.
Last year, in January, the highway was a "snoozer," meaning all paved except for a few short sections of construction and a little of wind blown sand. Even a Boss Hoss or 50 cc "postie" could drive it, unless pilot does something stupid (as the other guy I was with did three times ). To find any "tough stuff," or gravel, deep sand (except on a few sections where wind had blown sand on to pavement), rocks or mud, I had to get off the Pan American onto smaller roads.
Other than a few pot holes in places, dragging a trailer would be the same as dragging one through Canada and the USA except for when passing other vehicles, often moving much slower, and of course the issue of panic stopping or wind in Patagonia on Rt. 3 or 4 (and gravel tracks).
In 1997 I saw -0- Harleys (or Goldwings, or 1200-1300 cc "adventure" motorcycles). In January 2017 I saw, maybe, 100 or more Harley's (2-3 with sidecars), they were no longer an oddity. Saw no trailers being pulled. Did see one Harley (on his way from Chile to Bike Week in Daytona) in Nazca, Peru, that was scratched on one side and the pilot (not wearing his leather jacket which was tied on the back) who had some big sections of road rash on both legs (his Harley marketed jeans wore through quickly after he hit the pavement) and on his arms (he was wearing a wife-beater sleeveless T-shirt with only a leather vest on top of that), and on his fingers (from his fingerless gloves). His Harley helmet had some scratches, but no visible cracking. He admitted that he had "fooked-up," was having too much fun, not paying attention, and over cooked a tight curve, dragged a floorboard that lifted the rear wheel and he and the Harley slid down the road (he flip flopped) so not a road condition issue, but 100% "pilot error."
You can follow the South America leg of my 2017 trip with some pics of Colombia, Ecuador, Peru, Chile and Argentina, for free at:
www.greataroundtheworldmotorcycleadventurerally.co m
A final comment I would submit is likely your biggest "adventure" will be clearing Customs in Colombia if you do not speak Spanish, understand the concept of
"manana" (sp) and try to clear Customs on your own (and where you do it). Lot's of information on South America here on HU...just time consuming to surf and filter for freshness.
I'll close with this: Dave Barr flogged his old, tired, POS AMF H-D Sportster through South America 30-40 years ago, and he had no legs. Likely 100's have done the same (Pan American Highway) since then, at least through parts. It's not the make or manufacture of the motorcycle, it's the make-up of the pilot.
Regards, and the above is just my skewed opinion after six motorcycle trips around the globe
Dr. Gregory W. Frazier
Chief of the World Adventure Affairs Desk, CITY BIKE Magazine