Do you have under carriage braces spaced properly and do you have too much hang over on the ends from the bracing?
Wolmanized Treated Wood in most cases, as I have seen it come very wet and in most cases too wet. This has really caused me problems in keeping the gum off the saw blades.
In Texas, with the extreme heat, if the boards are not properly screwed down and no long overhanging, they will warp, contort, and perform all sorts of shapes during the drying time.
If I were you, I would consider making the table top from 2 x 6's and when you buy the wood, lay it out on the driveway very flat until it properly dries out. Then you should not have any problems.
If this is too much trouble, consider using Redwood or Cedar.
I build decks for a living and have to deal with this problem all the time. It seems that the wood is being shipped wetter and wetter each month. I wish that they would do a better job with this. The wood is great and the idea is wonderful, but it is just too wet.
Do you have problems with the saw blade binding? If so, keep some turpentine around and clean the blade periodically and this will save your saw.