I must agree it was a battle learning even the basics of Blender.
jPCT doesn't support dual sided polygon textures (which is good in a way, keeps things simple) so you will need to solidify the object as mentioned. Rather than copy the outer texture co-ordinates to the inner faces, you would want to simply apply white to the inside to mimic the light volume. You do this by selecting all the inner faces and either apply a white material from the materials menu on the right, or hop into texture mode, load up your texture, select a portion of the texture that contains white, then wrap that portion to the polygons you have selected. It's not easy to do so I wont go into it in detail, but there are plenty of video guides on youtube that will get you started.