Hi Sycamore. Outside the US going south the ATC situation can be very spotty. Taking a UH-60 to Brazil on a demo, we left Trinidad southbound to Manaus ( had the ESSS with 2-230 gallon tanks ) with a VFR forecast and a VFR flight plan. Wx turned very different and finally just south of the Orinoco River, down to 300 ft in rain where we could see down but not forward, we made a decision, climbed thru it ( well off airways ) and from on top at 12k we tried calling all the appropriate frequencies to file IFR. Not one response on all the VHF and UHF ATC freq’s. Finally a United Airlines guy heard us and thru him we got filed to Manaus. After landing ( Wx cleared down there and was clear and 50 ), went into the ATC folks to ensure we were cancelled and they had no flight plan for us. And there was no fuss about our arrival etc.( AOE).