After seeing your route, your choice of a front shock is a good one. I've only ridden the C&O from Georgetown to the Potomac Falls but even that short distance cries out for a bit of suspension. That said...

I hate trailers. But I only hate them for on-road touring. Off-road, they work better than panniers for the same reasons that I detail above. Bicycle suspension forks just don't work all that well when you put a huge load on them. It becomes a problem of sprung vs unsprung mass. Basically, the tire is a rubber ball that shock allows to bounce off the ground in a more or less controlled manner. Putting a lot of weight on the unsprung lowers reduces the ability of the shock to control the bounce by making it incapable of bouncing.

If you use a trailer in that situation, the fork (and other suspension parts if you have them) can work like they are supposed to. A trailer also lowers the mass on the rear wheel so that impacts have a bit less force. This helps keep the rear wheel being damaged over time. Trailers do have an impact on handling which is why I hate them for on-road riding. But for off-road, they are hard to beat. Get a singe wheel one, however. They more closely follow the track of the bike and you have one less tire to worry about.

A Tubus Swing, by the way, doesn't have the impact on the suspension like other front racks because it's not attached to the fork but suspended with the rest of the bike and rider. It's kind of kludgy and expensive.