I remember learning perspective drawing in art. It's served me well. The most important thing is to remember that all vertical lines stay vertical. Your tents look weird because one of the sides is perpendicular to the ground, making the tents appear to be the shape of a 90 degree triangle. Other than that, you've done pretty well. Keep practicing, try to add tonal shading, and try more complex things as you get better. I'd recommend finding a fine-tip pen for this sort of precision work.
