I stay at Twin Knobs a couple weeks in the spring and a copuple weeks in the fall each year. Great campground, well kept and very nice place to camp. This place has great campsites. I know loops 'A' & 'J' have electric campsites and trails to the waters edge. I take a boat so I don't know much about fishing in these areas but you can get to the water pretty easy. If you have a boat the campground has it's own ramp available to campers, or you can use the Alfrey ramp which requires a fee to be paid for it's use. There is also a beach if you are interested in that sort of thing.
The showerhouses are always well kept and if you look around you can usually get a spot within 2 or 3 sites of fresh water as well, as these are spaced frequently around each loop.
Each loop has a camp host and they, along with those who work the entrance are more than happy to answer any questions you may have. I am not sure but I think that after labor day they stop taking reservations so sites are first come first served, I know loop 'A' is always like that.
Zilpo is on the other side of the lake and I have never stayed there but folks that I know that have speak highly of it too.
No mention of a schedule but I think both of these campgrounds close for the winter at then end of October, I know for sure Twin Knobs does. If you Google these campgrounds there are several sites that incude the camping rules, schedule and maps that would help you plan a little in advance.
Hope this helps.