I am starting to gather information for our own south American adventure. did you find the pop up camper hindered your ability to stealth camp? or did people not really notice? we currently are deciding on a vehicle and camper configuration.
No, not at all. The biggest factor is the rig carrying your camper. A large set of testicles helps as well...
Go as light-weight as you can. I went a few km's off the beaten path just before dusk and never had a problem. I bought a used starcraft camper for 2,700 bucks off CL and it paid for itself 20 times over. It has a fridge, stove, storage, and a nice soft bed. I bush camped next to a french couple with a bed camper that had expanding sides and stood nearly 20 feet tall. They stuck out like a sore thumb and I was embarressed for them. Also, get rid of all the decals that are on most campers of today. I think they are totally useless and are made to attract majority of the herd. Make it look as much of a cargo vehicle as possible. I had a German tell me that I will run into issues with the high winds that are common in southern Argentina and Chile.... but I never encountered a problem worth noting.
Good luck!