The issue with the CDI might have been a little different from the radio shielding issue you're looking at for the antenna. A CDI box generates a lot of RF level noise due to the switching and high voltage. The big plate of metal might have caused some feedback of an interference signal from one part to another.

But then again the ESC's on electric models generate some pretty sharp high frequency signals and the harmonics from that are quite likely up where it could produce some issues. So all in all enclosing much of the gear in a similar configuration of metal is not a bad idea.

The thing with metal and RF is that it doesn't matter how thick it is. There is either metal or there isn't. What might save the day is if the various plates are not in electrical contact with each other. Or openings for such things as landing gear or wood wings or even the cockpit. All those leaks can add up to a metal fuselage that might not cause any signal degradation. But without testing it's tough to say for sure.

Acerc, any chance of some pictures of how you arranged your antenna on these models? I'm sure Kent and others would like to see what worked out well for you.