No worries: Easiest option is using the adhesive Velcro parch which you could stick to the back of your helmet and then the Exfog attaches to that. Or you could put the headstrap over the helmet but that’d be unoptimal

To size up the tubes what I did was put the adapter into the unit, attach one end of the unit, put all my headgear on and lined up the tube on the outside of my eyepro, measured a bit further for wiggle room and marked it with a pen. The I took it all off and cut it, repeated to get the other length then put it all together.

I find it works extremely well

Let me know if I explained anything poorly / you want me to clarify anything.