I have been told that 95% ethanol was the best solvent for preserving
specimens (specifically rotifers, but should apply to snails also) for
sequencing ribosomal RNAs.
 
Yes, the ethanol sold in drug stores is denatured. Undenatured ethanol is
subject to special taxes.
 
If rum is good enough for preserving specimens, I suppose the denaturants in
denatured alcohol can't be too harmful. The Merck Index gives a whole bunch
of formulas under Alcohol, denatured.
 
A.