If you're going to do this, I'd probably just use the varnish as the glue.  So brush on a thin layer of varnish on a section of the cover, then lay down your newspaper (are these articles about you? or about motorbiking? or just strips?) ... then brush on more varnish.  In this case you're using the newspaper as decoration rather than trying to make the cover sturdier, so you don't have to worry about layering.  Just do what looks best to you.  Then put at least one additional coat of varnish to protect it, probably more. 

Actually what you're doing a little more like decoupage than papier mache. 

Good luck with it, and let us know how it turns out.

Ok, thank you very much for your reply's. The covers are from hard plastic, it's not so flexible.

Which type of varnish should i use? Do you think, if i put enough layers varnish after it, it will hold against rain? (It will only see 3-4 day's rain a year)

If you look up the manufacturer of the covers online, what type of plastic do they say they're made from?  Some are ABS plastic.

Here is a how-to for painting ABS plastic that might be helpful:  http://www.ehow.com/how_4925502_paint-abs-plastic.html

It says that the surface gloss must be lightly abraded with fine sandpaper before painting, so the paint will stick. 

They say that you can use 'just about any solvent-based paint'.

I am saying 'paint' here, but I am assuming that the same conditions would apply when using varnish.  Here is some info on varnish and the types that exist:  http://en.wikipedia.org/wiki/Varnish.  Be aware that some varnishes are clear, some are tinted; some have a glossy finish and some are semi-gloss or satin.  The drying or curing times depend on the chemical makeup, some take longer so you would have to take care not to scratch the surface until it is hard.

Sue