Jonathon,
have you thought about the datalogger route. I have used a Digitron Monolog
single channel temperature logger which can take readings every, say, five
minutes. It is wireless, compact, so can be stuck anywhere. Then bring
indoors at required interval (weekly, daily etc) and download via serial
port to PC. Software allows graphical presentation of data etc. Only
drawback might be precision only quoted at +/- 0.5C.) If you want more info
or possible loan then e-mail me.

Dave.