I use finish nails driven at an angle thru the tongue. Glue isn't necessary. Prime everythng both sides and one topcoat before installation. When all wainscoting is on. The cap and base ( nailed into the studs )will hold everything tight then apply your final topcoat. I'm assuming your painting or varathaning. Priming and or painting before hand keeps shrinkage to a minimum and when it does shrink you won't have any unfinished wood showing thru at the seams. Hope this helps. This is the way I have always done it and it works well for me.