I found a small canner and have a silicone trivet that fits in the bottom, but it's solid--no cut-outs. Will this work OK or do I need one w/cut-outs to ensure even heating and water circulation? - thanks
I would use one with cut outs to allow the water to evenly boil
A traditional canning rack that fits your pot would be even better because it allows water to circulate all around your jars, which is important to ensure all organisms are killed and that you get a good vacuum seal. No trivet can equal the performance of a proper canning rack.
I agree totally with Diana, but in a pinch if you need a trivet (very important -- you don't want the jars resting right on the bottom of the pan as it increases the likelihood they will shatter) you can take the rings from canning lids and tie them together to make a trivet.
I think you really need a proper rack to hold the jars, lest they bounce around and possibly break in the boiling water bath.