All you need is some strip balsa wood, a pencil, a ruler (or other straight edge), a utility knife and a pair of scissors.
At 3/4" by 12" (and 1/32" thick), the stripwood is both long and too wide, so it needs to be cut. I measured and marked each strip into 3-7/8" sections, and I also drew another line straight down the middle of it. Each strip yielded 6 "planks" with a little bit left over.
There's one thing you should know about balsa wood: it's very weak along the grain, but not so much across it. Splitting it was easy; I used the utility knife to score a line down the middle, and then I simply exerted a little pressure on it to make it snap. Kinda like cutting plexiglas. Balsa isn't quite so fragile when you're going against the grain, though; attempts to use the score-and-snap technique resulted in… well, a mess. I used scissors instead. Worked like a charm (cutting along the grain with scissors is not a good idea; the wood will split in ways that you did not intend).
Next, I used wood glue to fix the boards to the MDF. I used the glue sparingly but balsa will curl no matter what. I've been working a section at a time, weighing the boards down with wooden blocks until the glue dries. This is what it looks like right now:
Interesting, isn't it? I'm not sure if you can see it, but I drew guidelines onto the MDF to ensure that I laid the boards straight. I'm nearly done the side of the porch, and then I'll work on the front. The corner is going to be a bit of a challenge; I'll probably need to miter the boards there. We'll see.
By the way, this picture does a good job of displaying the unevenness of the paint, doesn't it?
Once I finally get all the boards laid down, I can start the oh-so-fun process of putting masking tape all over the place again so I can stain the porch. Minwax has a nice gray stain that I'll likely use on the shingles, too. Then I can finally start working on the inside. Woot!