The point is, the Book of skulls is assigned to ALL your force (and so is the powerplant). So and you play those resources in a team with team bases? (which can't be assigned a resource?, if so, what happens, they're considered to be unassigned by the resource?

No you can't. The Book of the SKull is assigned to your whole team and a team base can't be assigned resources, so unfortunately this won't work.

yes you can

the actual ruling is that you can build your team with a resource no matter what character are in you theme, but if you bring a resource that assign all your character (BotS, Power plant), and you bring in the same theme characters that can't be assigned resource (like theme base, theme members or vehicles) there are no conflict, the resource assign to all, but except those characters

I have no idea what this means.

You cannot assign the book of skulls to a team that contains a team base.

never mind, i check again the post, crissdosmil confirm that you can't

Does this also mean you can't play a vehicle on a BOS team as well?

I'm not up on vehicle rules, but if they can't be assigned resources, then no you can't play a vehicle on a book team.

The Utility Belt and Phoenix Force would be the most common resources that are not assigned to all members of your force.