I've been looking into this for the 12ft flat bottom I recently picked up. There's very little online for people that have done this or kept it after they've done it and the general consensus seems to be "if you're having stability issues, get a bigger boat" : (
There's one good video on YouTube where a guy put two 10 foot 8 inch capped pvc pipes on the sides of his boat, drilling holes into the sides (above and below the waterline!) and used straps to keep it attached.
I've seen a few forum posts on iboats and a few other places where people did the math and 8-10 foot pvc about 6-8 inches in diameter would net you roughly 150-200 lbs of extra floatation, at the cost of moving through the water like a brick I'm sure.
The alternative if you don't want to drill holes is to rig up outriggers. these are REALLY popular among kayak and canoe paddlers (like me) because they're removable and add some extra stability. I haven't seen a lot of good pictures of them online but a friend and I used google sketch to draw up some pvc locks similar to vertical rod holders that would mount on the boat and use locking pins to keep the outriggers in place off the side of the boat.
Basically strapping a couple of water tight pvc pipes to the side of your boat will definitely add stability, but it looks ridiculous and the fact that in 10 years of tinboats and iboats there's like maybe six posts between them where people have done it, and I've never seen it on a lake I've fished, I'm guessing there's a lot of drawbacks.
Lastly, you can look into sponsons (the beavertail bolt on/weld on) pods that attach to the back of your boat which will add some stability if you're using a bigger motor.
That's everything I've found after about two weeks of google searches. Hope it helps.