No, it is not needed. You can simply pay by the night for camping. An annual pass covers the day use fees, not the camping fee.
It depends on what park as to what the fees are. Talk to the campground to find out what the fees will be for the time of year and length of your visit. I doubt it would be that much for a two week stay. Dad always got our family the passes because wr used to do A LOT of camping so it saved money. If you dont do a lot you wont need a summer pass.
I am not sure, your best bet is to call them directly or look on their website.
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