I’ve been woodworking for many years and have used circular and jig saws to follow lines to cut wood but sometimes I just want a little extra assurance that my cut will be a good one. So when it came time for the doors, I tried to use a straight edge whenever possible. The challenge is clamping it to the shell of the camper to follow the lines of the doors. Here is one way to do it (for certain lines). Another post will show how I managed it on the opposite side of the camper where clamps won’t work.
Since the window will be cut out later anyway, I partially cut it out to make room for clamps to hold a straight edge the right distance away from the cut line (for my saw). The masking tape is there to show the cut but also let me mark where to clamp the straight edge and remind me to stop cutting at the beginning of the top curve. It takes some time plus trial and error to set up but the result should be worth it, since the doors are one of the more ‘visible’ parts of the camper and you’ll see them pretty much every time you enter.