Could ethanol vapor collect in low spots?

Yes

Explanation:

Denatured ethanol fuel is a polar solvent, which is soluble in water. A

Polar solvent is a compound with a charge separation in chemical bonds, such as  alcohol, most acids, or ammonia. These have affinity with water and  will dissolve easily. Denatured fuel ethanol has a flash point of  -5 ° F and a vapor density of 1.5, indicating that it is heavier than air.

Consequently, ethanol vapors do not rise, similar to the gasoline vapors they are looking for  lower altitudes. The specific gravity of denatured fuel ethanol is 0.79, which  indicates that it is lighter than water and has a self-ignition temperature of 709 ° F and a  boiling point of 165-175 ° F. Like gasoline, the most denatured fuel,  the greatest danger of ethanol as an engine fuel component is its flammability.

It has a wider flammable range than gasoline (LEL is 3% and UEL is 19%).