Soldering will work, assuming you are using copper, not aluminum, but is not accepted as standard practice for code requirements. If you are in a city where this is a concern, just go get the correct hardware. I personally would not solder joints on a circuit that large.
As a side note, you should never "tin" the ends of wires that are going in to screw clamp terminals. With heating and cooling, the solder will soften and change shape, potentially relaxing to the point of coming loose and arcing.
-Cody