Film covered models can be painted with good results. It depends on the finished use as to what prep and paint to use. Glow/Gas need a lot more work whereas an electric model needs less.

Either way take time to iron or shrink down the covering to a smooth, well bonded finish. Wrinkles/looseness that appear after being painted are difficult to get out without damaging the paint.

Wet sand or burnish with scotchbrite pads to a dull finish then clean thoroughly with denatured alcohol or paint thinner. Primer may be needed if applying a light color over a dark one.

For an electric plane, enamal from spray cans work fine, even cheap cans from hardware stores or WalMart. A finish clear coat helps even out the color, especially if blending or doing camo schemes.

A glow/gas finish needs to be more durable. The same enamal can be used but needs a fuel proof finish such as TopFlite Lustercote. It is more expensive but using colors and clear in Lustercote provides a durable, fuel proof finish.

Of course there are other and often better paints to use if cost/space and time are not an issue.

As in any paint job, surface preparation is the key to success. I have used Rustoleum, WalMart house brand, Testors/Pactra and Lustercote. Some are fairly economical, others cost can add up quickly. Others may have better/easier suggestions but the above mentioned process has worked well for me.