My experience is that often campers will share a campsite with bicycle tourists. Offer to split the cost of the site and explain that you will camp away from them (if pitching a tent or hanging a hammock off designated pads is allowed). Folks in RVs sometimes enjoy the company for the evening. I personally would not worry about reserving sites in advance if you are bicycling solo or with one other. If there will be three or more, then maybe reservations are wise.