Your Panasonic might work if you can fit wider tires (I'd try 32's myself). It's packed gravel and packed dirt, but the towpath can get really muddy after a rain. I might try it on 28's with a light load. Search this forum for other C&O threads - there are a bunch. Go over to the COTowpath group on Yahoo groups - up-to-date info, trip reports, and lots of experience there. bikewashington.org has an excellent mile-by-mile section on the C&O and info on Scout trips. The councils that cover the towpath offer a patch and segments and publish a guidebook - I know the National Capitol Area Council (ncac) Scout store carries it.

On the 2 Scout trips I've been on, anything that could rattle or shake loose did. I would not suggest a seat-post rack for that reason. The one Scout with a FS MTB had problems with the vibration busting the mounts for his rear rack (we transferred everything to other bikes and got it replaced at the bike shop in Hancock. A rear rack that mounts to the rear axle for carrying the weight would probably hold up fine.

Are you going self-contained (better IMHO - more flexibility), or "heavy" with vehicles following and meet-up at one of the major campsites or H&B sites with road access? How many days? 1st trip we were self-contained and did it in 4 1/2 days with a resupply at Antietam. Second trip I joined up mid-way and the older Scouts did Brunswick to G'town in one day. vehicle support that time, so everyone traveled light on the towpath.