The previous owner took all of the windows out, riveted sheet metal to the frame, installed insulation inside, added furring strips, and then wood panels. I know I will be replacing the wood panels inside, but the sheet metal work looked well done, and he even used expanding foam to seal up the wall insulation tight. He added a few RV windows, and there are two more that come with the bus, but have not been installed yet.
Now that I know more about insulation, and it's importance, I will double check the previous insulation work. I have an infrared thermometer, and I should be able to get access to a thermal camera, so I will check for hot spots and thermal bridges. Also, I'm not sure I will add the extra windows. I've lived in Texas most of my life and I know how much a difference air conditioning makes. If it breaks for even one day, life suddenly feels unbearable. In every apartment I've lived in, I have always done thermal insulation projects. I add Mylar to the windows to reflect light out, I add clear plastic film to the window bays to cut down convection currents, I put up black out curtains, and I even put foam inserts into the wall and light sockets. I am usually able to cut my electric bill in half. On top of that, I have free energy at nights, so by timeshifting activities, and using lots of timers, having a window AC unit that only runs at night, I have been able to offload 59% of my energy usage to the nightime when it is free. (I pay above average rates during the day, but I use as little as possible, so I come out way ahead).