I own and am willing to do the work.

I do have a lot of vents closed off, to distribute heat to the parts of
the house that I'm using (bedrooms at night, living during the day,
etc.).

I will look into a manual damper, but where should I start?

G

Mark wrote:
you can put in an automaic or manual dampler that closes the duct to
the evap during heating season....

but even without a damper...if the air pressure is so high that it is
buldging the cover on your evap, then you may want to investigate
why.... do you have too many vents closed off, the back pressure
should not be that high...

Mark