Mona,
I too take them out the morning of shipping and usually by the time I write the address on the envelopes they are warmed up. I take mine to the post office as I ship a lot international; I have the custom slips here so I go ahead and make them out to save time at the post office.
When I did use the plastic baggies I always put a piece of paper towel in with the seeds, I did this as I packed them up to go in the fridge. This helps control moisture in the baggies when in the fridge because I have heard a lot of people say they have gotten mold in the baggies because of moisture. And this would help with any moisture during shipping as well.
If you are worried about shipping in the heat you could say you will ship them in the fall once it cools down. There are sellers on the LA that won't ship in the winter either because they are afraid the seeds will freeze.
