Let me fist say,I've never stayed at or am familiar with these campgrounds. Now having said that,I did a search on woodalls for campgrounds that accomodate big rigs and are within 25 miles of Leabanon, NH.
There were 3 and their websites are 1. www.mascomalake.com
(closes mid Oct) 2. www.pinevalleyrv.com
(closes last weekend in Oct) 3. www.lakechampagne.com
(closes Oct 15). #2 + #3 are in VT.
Not sure where you live or are coming from but unfortunately for those of us in this part of the country the camping options are almost non-existent after Columbus Day.
Hopefully someone that has camped in this area will respond soon.