you *could* use LN, but you'll never get the track back up (without ruining it, that is).
Like Concretelackey said, general consensus is the cheapest latex caulk you can find (DAP is pretty good, and easy to find in most hardware/home improvement stores. Goes for about $2 a tube here for ones that fit in a caulking gun, and a little less for the smaller "quick-fix" squeeze bottle) Lay down a small bead, spread out really thin with a putty knife, lay the track, cover with bricks/old MR mags/anything else heavy enough to keep the track in place, wait about an hour for it to set enough to do a test run, make sure everything is working right, then put the weights back on top overnight. General reccommendation I've seen here is to do about 10-15' max at a time (eg, lay 15' weigh it down, move on to next 15', continue on til you're finished for the evening(or run out of weights)).
-Dan
Builder of Bowser steam! Railimages Site