Keep in mind that these are the "pen and paper" design specifications. The real-world is somewhat different. You need to remember that the panel specifications are determined in a special test chamber held at a specific temperature (25C) with an artificial light source producing exactly 1000W/square meter.
In the real-world though, panels will rarely, if ever produce their rated output. That's because the sun at the earth's surface is not exactly 1000W/square meter, and the panels are hotter than 25C. From empirical testing, I've routinely used 85% as a "de-rating" for the label specifications. If you go through any of my other posts where I do solar production calculations, you will see that 85% value popping up over and over.
So, what will give you an honest 40A while charging at 13V, the math is..... (40A X 13V)/85% = 612W. Call that two 300W panels.