I made the decals using water slide decal paper from the hobby shop. Can't remember the brand name but they sell types for inkjet printers and laser printers. It comes in clear and white. If using the clear you must apply it to a white surface because the colors printed on it are transparent as well. The white paper is very thin so if applying it on a color other than white you may want to double it up or back it up with a white background. After printing the designs, letters, etc., let the page dry completely and use your favorite fuel proof clear spray (Lustrekote is what I used) to coat the printed page. Make sure your coverage is complete by doing about 3 light but thorough coats because the inkjet ink is water soluble. After drying you can then cut the designs from the sheet and apply them by soaking in a bowl of water and sliding them into postion on your plane. I brushed some of the clear around the edges to seal them to the Monokote. Over 20 flights so far and they still look great.
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