i know cmon has a nifty lil guide for lava bases, hold on and i'll dig it out...
http://www.coolminiornot.com/article/aid/507 http://www.coolminiornot.com/article/aid/365/page/1
actually, they had two! bonus!
as for the sandpaper thing just get the finest grade you can find, although a needle file works just as well if you have one (and if not, why not!?)