Toady at the grocery I was looking for an alternative to wax paper (Since yes that did rip into little pieces). I tired to line with saranwrap but that was a big 'ole mess.
Anywho when I was about to give up I saw a box of Reynolds Slow cooker liners. They are 13 x 21 inches. Since they can be heated to fairly high heat they dont melt when you pour your soap. I'm sure you could rebatch in these too. How easy would that be! Just line your crock pot with the bag, come back when it's all melted, snip a corner of the bag, pour in your mold and you can just toss the bag, no mess in your crock pot!
One bag (when cut) lines my mold (a 9 x 4 inch liquor box

). I'm going to see when this batch comes out if I can wash and reuse. They do cost about $3.00 and you get 4, so it's not the best value I must admit, but very handy and easy to use! And if you can reuse then I guess they would be a good value. Maybe save a liner for each scent, since that will probably absorb into the plastic.