I just tried this on my fully updated LXDE box. Like you, I use checkgmail and prefer to use the Chromium browser because it's faster and doesn't have the "freezes" that I've experienced with Firefox since version 3.2, where Firefox just freezes my computer for up to a full minute (related to pages running scripts, I believe).
Sorry to get sidetracked ... under checkgmail, enter your browser command line as "chromium-browser %u" to open Chromium with the Gmail login page displayed. For some reason, Chromium will not accept the login password that was entered into checkgmail, and forces you to re-supply your account password before displaying your email. I guess you could look at this as an added layer of security for your email account. I personally don't find it all that much of an inconvenience to have to re-enter my account password. Note that you have to have the space before the %u in the command line.
I hope this helps!