the thermal scan is very effective, even
more so when used in conjunction with
a blower door.
Cost would be a concern.
Get your home and duct work tested
with a blower door.
Identify the leakage areas to be sealed,
you can use a lot of calk and miss the
leakage areas if you do not know where
House leakage is identified by depressurization
test with blower door, duct leakage can also
be identified by pressurizing with blower door.
I use smoke sticks for both types of testing
to show homeowner/builder/havc installer
where leakage areas are.
Best of luck.
BTW the bugs come in everywhere.
In my area ants are a big problem.
Caulking plumbing penetrations under
sinks is a start!