my idea for a self watering flat from buckets

I have an idea for a self watering flat. It would use two of the plastic buckets which are so easy to get a bakeries, etc. The first bucket will be cut down to three inches. This is the flat. The second bucket will be left intact, and the cover put on. The "flat" will be placed on the top of the covered bucket, and holes drilled through both the bottom of the flat and the cover of the bucket. Then cotton rags will be threaded through the holes, tight enough that they effectively join the two pieces. The bucket will be filled with water, the flat with potting mix, seeds will be planted, and some plastic used to cover the flat till the seeds sprout.

Does anyone have any ideas for improvements?

That is what we call a SIP, or sub-irrigated planter.
Not sure how well the cotton rags will wick, most designs use peat soil or sometimes nylon rope.
Definitely worth a try, could save time/money.