Flip-
Dave's got some very good places to start for you, as there are links to most all of the local marinas and sources right there.
Lewiston Lake is a regulator lake below Trinity Lake which serves to let out a constant water output whereas the big lake upstream can put out more or less water based on power needs during the 24 hour daily power cycle.
Lewiston Lake is a pretty shallow lake on the very upper end, but for the most part it's just fine for a C-Dory. There are large trout, and you'll want to get in tune with the local fishing informtion for the time of year you'll be there. Sometimes summer fishing can be a bit difficiult for new boaters to the lake. Be sure to talk with the local fishing shops when arriving.
Trinity Lake is like close to 30 miles long from the dam all the way to the upper reaches. It's about 2300 feet in elevation, but still very warm (95++) during the summer days, and can be windy. It has lots of smalllmouth bass and trout. There are plenty of marinas as well as public launch ramps, campgrounds, and resorts.
From Redding, you have to pass over winding Buckhorn Summit (3200 ft) and back down Highway 299w to the Lewiston cutoff. No big deal, but it's about 45 minutes to the town of Lewiston, another 15 minutes to Lewiston Lake, and then another 15 to 30 minutes to the lower reaches of Trinity Lake, but you'll already be in the town of Lewiston for the reunion. Lewiston is a colorful gold rush mining town just below Lewiston Lake. It has its own special charm, being a mixture of before the turn of the century (1900) dwellings and more modern retirement homes. Character and contrast abound! Very rural and low key. Check out the fish hatchery just above town.
If you have a lot of stuff to buy, you might do it in Redding beforehand, as the shopping alternatives in Lewiston are a little limited.
Joe.