If you can give yourself PLENTY of room in front of the loading door, 18" is code but it isn't really a lot of space. Eventually something always falls out. I just finished a fairly large (44" x 72") flush pad for my new Fireview. Went down to the subfloor (actually replaced it as well, it was cracked), put on one layer of 1/2" Wonderboard, and tiled with quarry tile from Home Depot. The quarry tile is very strong (a little bland in color though). I'd recommend the Wonderboard or Durock as they are known to take the temperature. Be careful and look a the edges, H-D has something called Perma-Base that has foam beads mixed in - no good. Scoring the Wonderboard is pretty straightforward, Mark it , lay it on a working surface, use a 2 x 4 as a straightedge and score it a good 10 to 20 times, hard. Flip over and repeat. You have to get through the fabric - on BOTH sides. You do this it just falls apart. A comment on tiling and grouting for the DIY crowd: Thinset that is hardening while you're placing tile is an inherently stressful situation. My project was successful; my wife hasn't left me (and she helped!), the kids didn't run away. Good luck!