It's a little more malleable than Romex and you don't have to strip the plastic coating and paper off like you do with Romex so its little easier to work with. That said, if you already have the Romex lying around, I wouldn't go out an buy the soldering wire. The Romex will work fine. I actually ran it around the inside and it worked fine for me, but the outside approach actually seems easier to me. It's really only a starting point though and found that a lot of small adjustments is really the key. Once you cut the foam with a serrated knife, I suggest high grit sandpaper or a surform tool (also at Home Depot, critical to outfitting IMHO) to make the minor adjustments. I've also heard somewhere (and truly believe this) that this a Sunday morning/coffee kind of project vs. a Saturday night/beer activity. So, take your time and it'll all be good. Bob Marley in the background helps too.

Enjoy.