I am using an electronic cigarette and the liquid may contain propylene glycol. Will this test positive on an EtG test? I am being monitored bi-monthly and am pretty paranoid about false positives.

It should not and there is no record of false positive to date. However, PG is an alcohol, it is metabolized by Alcohol Dehydrogenase ADH (same as ethanol) and about half is excreted as a glucuronide conjugate. My only worry would be a cross-reaction with EtG at the level of initial screening.

I am not at all familiar with e-cigarettes and don't know the quantity of PG contained. While it is unlikely that you would test positive it might be wise not to use the e-cigarette for about 12 hours prior to testing.

Don't believe it is a problem but there is no research that has specifically tested the reactivity of the various alcohols.

You are well advised to be careful when exposed to this test. There are thousands of environmental sources of ethanol that can cause a positive read.