The lightmap tutorial on the wiki also seems to be outdated...
I don't know what wiki tutorial you looked at but the lightmap tutorials are not outdated. For sure multi-channel lightmap is not outdated.
There are a couple another method for interior lighting such as material lighting and procedural lighting.
The Space Shuttle, c172p, J3Cub/PA-18 and a host of others all have interior lighting you can review for examples.
I tried to bake the lighting into the interior texture
Yeah, that's not going to work. Changing the texture to pure white with no light cast on it is still not going to refract any light.
Kansas and Ohio/Midwest scenery development.
KEQA, 3AU, KRCP Airport Layout
Intel i7/GeForce RTX 2070/Max-Q