This is a very common issue. As a Cubmaster I deal with this from every Den level. The idea is that you plan an event far enough in advance that all can make it. But... you are not obligated to keep rescheduling events for those who don't. You will find that those 5 chapters go fairly quickly and you will have time to visit additional places later in the year.
Several Den Leaders last year approached me with this question and were frustrated they couldn't get more participation at their planned outtings. Eventually, when the boys that came ended up with their awards at Pack Meeting and th