Bought an inexpensive ($14.95) Oregon Scientific lighted int/ext thermometer/clock/alarm clock and thought I'd share this minor project's installation.  The unit is velcro'ed to the rear cabinet.  The exterior temp sensor has a 10ft wire that is routed up and over the top-then-back of the cabinet, down beside-then-under the rear seat, and out through an existing grommet-protected hole.

The whole thing only took an hour or so; mostly trying to figure out where to route the exterior temp sensor to be effective but w/out drilling holes in the van, or disassembling more than I was willing to make this work (i.e. semi-lazy project).  Overall happy with results.  Yesterday it was 66F outside (Seattle area), and the van sitting in the sun for three hours produced an interior temp of 98.6F.  Will be interesting to watch during camping trips over the mountains to hotter eastern Washington this summer.

http://tinyurl.com/32ddm6d

ToddB
91 Westy Weekender
94 Audi 90CSQ
07 Beetle Conv