The round hole looks like someone has in the past had a stove for heating. To me it looks like were the flue came through the wall. This is not a normal place for a hole in your trailer.
Since your photos do not let us see which side of the trailer the holes are on or which end is the front, it is difficult to give advice. I'll guess that square hole is were the furnace was removed.
Those lights that can be seen through the window are not original to your trailer. All lighting was originally 12v
. Those lights appear to be 120v.
My advice is to get someone who has experience to help you evaluate the cost of renovating that trailer, before you go further. You are looking at big $.