Nice to see some risers being put down Steve, I've used wood screws to hold them in place while the adhesive dried , just used the drill to screw them right through the styro and actually think I left some in. Just a bit of an idea Steve , for myself I working on this second layout I found it better to cover the riser tops over the gaps with plaster cloth or something along that line so that the scenery wouln't fall thru. I did this right over my roadbed or was it under it geez can't remember now but it sure helped in the long run, just a thought of course. 
