I know a few people who have good success using a FRIO case with insulin pens:
http://www.frioinsulincoolingcase.com/ and
http://friouk.com/ and available from multiple vendors.
I have had good success myself with a FRIO for other medications, but have not had to store insulin.
FRIO has pretty good info about what temps the devices can accomplish, how it is used, etc. Using that plus info from your medication manufacturer and/or pharmacist about the temp ranges you need to keep the med in (and there can be a difference between long term storage and shorter term usage for some meds) should let you know whether the FRIO is appropriate to use for your specific needs or not. It won't work for all meds, but it does work for many.
Finally: a reminder that medication should be kept in carry-on baggage, not checked baggage. In addition to the (usually small) risk of it taking a temporary little vacation or permanent trip elsewhere, checked baggage experiences extremes of temperature and pressure that can have a negative effect on medications. Not to mention exposure to the elements sitting on tarmacs and such.
SW