I'd use epoxy. Thicken it a bit with Cab-O-Sil. Wipe the teak with acetone to remove the surface oil. Space the slats a bit so you can fill the gap with epoxy/graphite. One C-clamp on each end of each board should do the trick - you may want to run a wood strip over each slat with a spacer in the center to distribute the clamping force. No need to glue them all at once if you're short on clamps. Did a similar job last year - teak over glass/epoxy covered foam board. Came out fine. I used 3/16 teak slats which worked out OK - 1/4 inch will give you a bit more allowance for planing/sanding smooth.