My house is a C.P. Morgan home that has all flex ducts ran off the plenums, supply and return, with no trunk lines. Would it be better to run the trunk lines off the stacks or can I get adequate airflow without doing all that work and money. I already got all of my sizing off the Manual J and D. Any tips on doing them to save a little dough... especially the returns? Should I insulate the ducts... they are in the attic.