I made some templates for gels to use on the Godox AD400Pro and AD600Pro (as well as most standard flashes and AD200 Fresnel head). These gels will easily slip over the flash tube and allow you to use any modifier while using the smallest gel possible. They have vent holes that generally line up with the vent holes in the protective cover of the flash tube.
Print them at 100% on 8.5×11 paper and cut them out around the outer edge. Use it to cut out the gel from a Rosco or the like gel sheet.
Punch a few holes around the template in solid white areas. Put weak tape over those holes so that the template sticks to the gel and doesn’t move as you cut it.
Once it is cut, use an 8mm hole punch for the vent holes. This one worked really well. I found that it cut much cleaner by having paper on one side of the gel. So if you are re-using a template, just slide a scrap piece of paper in when you punch it.
Once the gel is cut and punched, tape the long part end to end to form a circle.
Press it flat directly in the middle of the top part.
Then fold the top circle in half and press it flat. Tape the small flap that comes down and touches the body of the gel down.
This will then give you a gel that stores flat but slips over the flash tube cylinder. Once you slip it on, use a 2″ silicone cooking band around the top to hold down the other tabs and keep it on the tube. Rotate it around so that most of the vent holes line up. I also add a label at the bottom so that I know which gel it is in case I need to make another or need to distinguish between similar looking colors.
Right click the links below and click save link as to save the templates.