You'll definitely want that template to get the holes drilled in the correct place. Make sure you orient the template, it hugs the lines of the box. I'm away from the bike, but of I recall the bolts secure the back rest from inside the case. I did use the supplied washers and added some silicone around the holes to insure no rain gets in. I don't remember any plugs?
Cam
PS - The back rest mounts to the LID of my HB box. Same with the Givi I used on my Calvin.