Why is this place open three months a year?I'll never understand why,it's a museum, every other museum I've ever been to isn't closed as much

Most likely for two reasons. It is a fully uncovered museum which means it gets all the elements inside. Also, I believe the workers may all be volunteers. However, I'm not totally sure on that. I would agree with you that open for only 3 months a year is definitely a short amount of time.

We just used the RV park for a couple of nights.