Do you care about indexing? These would work very well, Dia-Compe ENE Down Tube Shifters - Shifters - Shifting - Components

I prefer bar ends for touring but I've used downtube shifters extensively on tours and they work well.

If you want indexing, 9 speed downtube shifters will work well. Amazon.com : Shimano Dura Ace Downtube Shifters (Silver) : Bike Shifters And Parts : Sports & Outdoors

One of the comments on the Amazon webpage is from a customer who mounted these to his or her Surly LHT.

I rode my Bridgestone RB-1 yesterday which has a triple and downtube shifters. I had forgotten how nicely downtube shifters work. Downtube shifters have a really nice positive feel to them over a triple.