I have made some in the past for a canoe of mine. I used pool noodles for flotation. At first I used 1 noodle on each side about 4ft long. It added some stability, but not enough for me to stand up. I added a second noodle on each side, and that gave considerably more stability. Other options I considered was using boat fenders, but noodles were cheaper... Sorry I do not have any pictures anymore.
Basically I bought the thickest fun noodles I could find... I think had about a 5" diameter with a 1" hole through the center. I ran some electrical conduit through the center (PVC would probably work well too). The conduit was 4 inches longer then the noodle, so 2 inches protruded on each side past the noodle. I drilled a hole through each end of the conduit and ran a threaded bar through the hole and used nuts to tighten it to the conduit. I attached the threaded bars to two 2x4's which I ran across the canoe, one towards the front and one towards the back. I made the threaded bars about 12" long, and attached them to the 2x4's with wing nuts so I could adjust the height of the floats.
I only used them 2 or 3 times, but everything worked exactly as it was suppose to. The floats and 2x4's where as long as I could make them without drastically hindering the ability to paddle in the back and front seats. Ultimately, it was an improvement to no stabilizers--and cost me about $40 and maybe 2 or 3 hours to make them. If you want pictures, I may be able to find some... the pictures really tell the whole story
It would take about 8-10 minutes to assemble and disassemble it by myself... I basically transported it in 4 sections (the two 2x2's and the two floats w/ hardware)
EDIT: Pictures Found on my old abandoned Myspace page!!! This was before I added the second stabilizers on each side. Simple drilled another hole in the 2x4's and added them inside the existing floats.