Dreaded P0442, P0455 on '02 TJ Sport

Okay, so warranty expired a few months back
and now I start getting the dreaded P0442 and
P0455 MIL errors (small and large leaks in the
evap emissions system). I have reset the
computer several times and they keep coming
back - no other errors though.

So I want to start by replacing the gas cap as
some have suggested elsewhere. Local dealership
(the only one for 150 miles in any direction) wants
$20 and they would have to order it! Is there
anywhere online I can get a factory gas cap for
a reasonable price?

What other things should I be checking related
to these codes?

Any ideas greatly appreciated . . . JELo