Originally Posted by Carbonfiberboy

Thank you! Since I started this thread, I've done quite a bit of web research on tire compounds and reviews of wet weather performance. I've compiled the following list of tires from this research:

Avocet FasGrip SL K
Michelin Pro3 Grip
Vittoria Open Pave Evo CG
Vittoria Diamonte Pro Tech
Vittoria Rubino Pro Tech
Vittoria Revo KXS
Continental GP4000S - note this is the "S" or Black Chili rubber version, not the standard 4000
Schwalbe Ultremo
Continental GP4Seasons - good wet stiction, but high rolling resistance so may be appropriate for rough roads.

The particular models indicate special tread compounds. For instance, the Vittoria Corsa Evo is reportedly bad in the wet. The "Tech" in the Rubino model indicates wet weather compound as well as sidewall reinforcement.

Unfortunately, few of these tires come in widths that we normally associate with tandeming. The Rubino Pro Tech does. And some come with sufficiently high pressure limits to make them entirely feasible.