Ilikeplanes,

There are probably as many different methods of doing this as there are modellers

I have used epoxy, ca, pva, and old fashioned balsa cement for this - preference for wings under 30" long is very slow ca, over that I use 30 minute epoxy.

FWIW the way I go is this -

Sand LE so that it is properly faired in with the ribs (IE NO STEP!!).
Mark rib positions etc on inside of sheeting.
Give sheet, spar and rib surfaces one coat of weak dope to seal. Dont sand off - you want the roughness on there.
Apply adhesive to both surfaces - the less the better.
An old rubber motor gives an excellent supply of instant compression - pins in the building board only and strap it on...but rubber bands is a second best. Go diagonal rather than chordwise to prevent gluing hills and valleys into the sheet.

The secret really is (IMHO) to use an adhesive that is strong enough to do the job and at the same time will have a "pot life" sufficient to get the sheeting properly in place.

One of the big tricks to making this easier is to take the sheet out over the top of the le, rather than trying to make a cabinet and rebate the front edge.

Does that help?