I highly recommend cresties, they are tame and easy to handle. Mine eats repashy and gets fed pheonix worms twice a week. I use an Exo-Terra now, but I had mine in a 20H with just a normal screen top. If you want you can stand up your 20g on its side to get the height they need.
This site is great and covers everything you need to know. http://www.ciliatus.com/content/index.php?option=com_content&task=view&id=28&Itemid=175
This site is great and covers everything you need to know. http://www.ciliatus.com/content/index.php?option=com_content&task=view&id=28&Itemid=175
. Sand is something you have to take some precaution with though.