I dont have tank cover..but this site might give u some insite on them.. Many tank covers do need to go under the gas tank though, becuz they are not generally something that you would take on and off very often. so once its on, people generally leave them on.
http://www.targa-acc.com/main_powersearch_nf.html
http://www.targa-acc.com/main_powersearch_nf.html