Thanks ny biker and Jolt!
Since we are trying to keep our possession count to a reasonable level (since we might go full-time RVing someday), I think we're going to go with the tires idea. I like the Bontrager LT1s. I'll always have the knobbies I can put back on if needed.
I just knew the TE gals would come through on this one with a solution I hadn't even considered! 
Thanks again!
Emily
2011 Jamis Dakar XC "Toto" - Selle Italia Ldy Gel Flow
2007 Trek Pilot 5.0 WSD "Gloria" - Selle Italia Diva Gel Flow
2004 Bike Friday Petite Pocket Crusoe - Selle Italia Diva Gel Flow