Wallpapering directly to walls or to posterboard first?

I had an idea about wallpapering - it's going to be difficult working
in such enclosed spaces, (though the gable is done already - I did
that portion prior to assembly - I KNEW I'd never be able to get
inside there) and I was wondering how I was going to hide some of my
(ahem) messy electrical tape runs, and the eyelets.

Someone suggested putting scotch tape over some of that, and I can do
that, but... what if I made posterboard plans of the walls, made sure
they fit perfectly, wallpapered that, and then when it was dry,
affixing it in place, perhaps with wallpaper paste.

There are some advantages:

1. Working in a non-enclosed space would be much easier.
2. It would be easier to correct mistakes (throw away the posterboard
and start over if need be)
3. It would better cover the flaws in the walls like bubbles in the
electric or whatnot.

However, I'm sure there are disadvantages, but I'm not sure what they
are, not having done this before. Is there anyone who has used this
method? What are the pros and cons?

Any advice?

Cathy Weeks