There's a beautiful pine-woods section in one of the 5 campgrounds in Peninsula SP, Wisconsin - should you ever head that way.
A second on Ponderosa SP in Idaho!! Love that place! The RV section has big sites and full hookups (amazing for a state park) and the "feel" of pine trees throughout.
NFS campgrounds in Island Park, Idaho (Buffalo, Upper Coffee Pot, etc.) - some with electric hookups, some without.
Not pines, but Seeley Lake, Montana has some beautiful wooded sites, as do some of the campgrounds just west of Glacier NP.
Collier Memorial State Park in Chiloquin, OR has some lovely wooded sites. Not far from Crater Lake - a bonus.
Colter Bay RV Park, Grand Tetons - spectacular! (And hookups, to boot!)
Agreed also on the (far) northern California redwoods area.