Alternator issues

So, I have a Nomad. I am having issues with the electrical system. I have only had it for a few months and have been plagued with dim lights, no turn signals, dead batteries, etc. Currently the alternator and battery are new. Things have been working well since the install until today. Driving with headlights on and heater on I started to get symptoms of bad alternator this morning. Sure enough would not start, once I got to my destination and turned it off. Belt seemed a bit loose, tightened it, got a jump and all seemed well. (Figured it was not spinning alternator right) Went to lunch and back, no issues (also no headlights or heater on). Driving home tonight, same symptoms returned (with headlights and heater on), this time the belt was not loose though. I am out of ideas as to why it wont charge suddenly. First time I used the heater was today. Maybe that? Cheap Walmart radio installed a couple of months ago.