Smallest most compact RF modulator?

[Trekintosh]

Hi guys, I'm new here. I've got a passion for ~5" portable color tubes with AV inputs, but recently was gifted a lovely 13" Sharp Linytron Plus and was thinking about sticking my spare unused Chromecast inside to make an all-in-one package.

However to get there obviously I need to uncase several components and make the smallest device I possibly can inside the TV. So what's the smallest RF modulator I can find to stick inside some spare space? Getting HDMI to composite is easy and cheap, tiny active converters are common for $10, and they run on USB power so it's easy to tap into whatever power supply I find for the Chromecast, however most RF modulators I've seen are fairly clunky.