framing basement with 2x3's...PT baseplate???

Have you tried a lumber supply company? They usually have a bigger selection than the home centers. If they don't have it, they can probably rip it down for you. While there you should compare prices for all of your lumber needs and take a look at the quality of their inventory.

Use plastic wood. (trex, or something similar.) You don't want to rip PT lengthwise, the treatment isn't full depth. Alternatively, you could use a regular

Or turn everything flat so you've got 1.5" deep walls. Note that if you do this, you'll have to armor all your wiring, because it won't be the expected 1.5" from the wall surface.

You lose insulation while gaining a inch:(

It is entirely dependent up what the local softwood framing lumber species is. Douglas Fir does not absorb the treatment chemicals well, even with incising, so it is proper to treat all the cut ends. Southern Yellow Pine, on the other hand, absorbs the chemicals so well that it is not incised, so I believe treating the cut ends is not needed in that case.

Cheers, Wayne

What about using a regular 2x3 and putting something under it like plastic or sill foam?? Anybody know what the national code (IBC?)says?