Rivits!--some bloody big Rivits!
OK---seriously now----
90% of modelers you ask (even the modellers) will say white glue--most of them will say dilluted with water. A few may reccommend a specific product(same thing) made for the purpose--like the one from Woodland Scenics----I would recommend the versatile , strong ^&^ convenient
Spray Adhesive from 3M called Super #77 Spray---give it a shot