Don,
I agree, the KOA is a nice park, but it is a long ways from anywhere; and if you are going to the caverns from there, it is really a long day. You will need several hours to visit the cavern.
We stayed at the
Carlsbad RV Park and Campground. This place is nothing special, but the staff was very friendly, and the cost fit our budget.
Don't even think of staying at the RV Park at the entrance, White City, it is a real dump.....doesn't seem very safe either.
The Carlsbad Caverns are wonderful; you might want to check to see when the bats are there, think they only open that area during certain times.