have a Hunter HDV31 direct vent gas fireplace and since Hunter went out of business and was purchased by Monassen. I was told to buy Monassen's direct vent termination kit. It comes with a 4 foot flex vent and I need 12 feet in total and the company gave me a 10 foot flex vent and told to attach together with inner and outer adapter that is included in the kit. Is this acceptable to use that vent kit and attach the 2 vents together. The instruction is unclear on attaching the 2 together.