Interior upgrades, how to attach to roof on inside

anyone attach accessories to the roof on the inside of the van...through the headliner?
I'm wanting to make some custom storage bins and also attach some LED gooseneck lights in the back.
can you only screw things to the support crossmembers?
is the roof itself single layer or double layer?
i'm guessing i'll only be able to screw directly to the crossmembers, unless i run intermediate metal strips in between each cross member.
i just dont want to penetrate my roof with a misplaced screw.

i'm estimating i'll be safe with probably #8 3/4" screws, screwed into the crossmembers.
anyone done anything like this?

thanks