These days most people are using pond foam beckets makes some and its available at HD, but great stuff makes it as well as touch and foam. Touch and foam landscape foam is what I used mainly because it is $5 cheaper than beckets from HD. I found the touch and foam at a True Value hardware store they sold the brand but they had to special order the pond foam.
Here is a pic of the tank no water yet.
<a href="http://s1073.photobucket.com/albums/w390/NeptunesTender/?action=view¤t=cavepic.jpg" target="_blank"><img src="http://i1073.photobucket.com/albums/w390/NeptunesTender/cavepic.jpg" border="0" alt="cave pic"></a>
HTH,
Ed