Air Conditioning Duct

[starfishkiller]

I am installing air conditioning on my 33' CC. There will be a few long straight duct runs. The installation kit came with flexible duct, which is essentially 4" drier hose. I have been thinking about using 4" schedule 35 plastic pipe for the long straight runs. I am not sure if the flexible duct will fit over the schedule 35 pipe. Has anyone done an AC installation. Anyone tried this or used something else for the duct pipe.

thanks

eric