FYi you can easily swing up to Carlsbad from Davis Mountains SP and the KOA is a nice KOA. Two nights would cover your trip up with a swing by the Guadalupe Mountains National Park to check it out,and then a day of the caverns, and watching the bat flight that evening, that was really neat. Of course you may want to go further to Roswell and see the aliens
I will tell you the KOA is not right next to Carlsbad Caverns maybe 30 minutes or so. If I remember correctly.
Rest is hard to say try to be there (Davis Mountains) when the do Star parties,
McDonald Observatory
and visit during the day for uniquie view of sun spots.
I would say start thinking about reservations sooner rather than later, it can't hurt to have them once you know you are going.