I have found that double sided tape works the best for this.Just tape up the perimeter with tape and start with a corner.You can get it perfectly flat no wrinkles or bumps.I am sure Hams way works great also.I wouldn't think that after the glue is dry it would put off any fumes harmful to the plants, and if the lights are hot enough to heat the glue up behind your mylar then you have bigger issues than mylar .IMO