Thanks so much for your suggestions.  I used an unfinished spruce for the bed with a layer of drywall on top as suggested in one layout book and attached the track directly on top of that.  Changing to the pine and sealing it might help.  I've got a de-humidifier now for the summer months so that should also help.  As I really love the realism with model railroading, it sounds like I should stick with what I'm currently using.   Woodland scenes sells their foam trackbed and I've heard it's supposed to help in this regard.  Has anybody used this and what do you think?

I have had a 4' x 10' set-up for just over a year now (my second layout since beginning the hobby).  We have recently re-done our basement and I now have an area to permanently set up a new and larger layout.  I have two boys getting hooked on this hobby along with myself so I'm trying to please all three of us.  I am an avid crafter and artist so making buildings and scenery do not trouble me, but track does.  My current set-up has Atlas track permantly placed.  However, we heat with wood in the winter and the temperature fluctuations are a real challenge.  I'm really starting to have to trouble with the track and I'm wondering weather or not a system like the E-Z track will hold up better under the expansion and contraction because it is attached to its own trackbed.  If I do go with the E-Z track, when constructing bridges and such, does the track come off the road bed?  I know Bachmann has an E-Z track layout book.  Would this be a good investment?