You can try it out with 4SALE (http://4sale.bioapps.biozentrum.uni-wuerzburg.de/).
It does not compare the structure side by side but rather give you a consensus structure and the differences of the base pair will be indicated with different colors.
The simplest quickest way I know of to draw a reasonable looking secondary structure. Do you have structural data for the mutant RNAs or do you want to predict structural changes?