Much like your contractor, we are perplexed as well. The thermal insulation properties of ThermoClimb should prevent most hot or cold air from moving through your attic opening. We recommend that you use silicone sealant before you staple or screw the ThermoClimb onto your attic frame.
Don't know what happened to your manual! Here's the manual, https://remingtonsolar.com/wp-content/uploads/ThermoClimb-Installation-Guide1.pdf which is also located on our website.