In reply to RKernan:
I used a FreeLoader with the supercharger add on panel to succesfully keep a copmact digital camera, a mobile phone, an MP3 player and a couple of AA rechargables topped up for 3 weeks on a cycle tour not long ago.
I think if you want to charge higher drain items like VHF radios, sat phones and DSLRs then you will need both a bigger panel and a bigger storage cell - which means a bigger price tag.
You are only going for 4 weeks so you may find it easier and cheaper to use disposable batteries. You can get AA trays for most good VHF's and many Sat phones. take a camera that loads standard NiMh or Li Ion cells