hope to ride near you some day...I run the Delorme USB cable into my tank bag which has a cig lighter socket. In the socket there's a Verizon phone car charger with a spare USB port "MiniUSB Dual Vehicle Power Charger w/USB Port". Phone is in the map pocket. Phone/car cable is another option vs the cig to 2 USBs.
I did have some issues when synching the PN60 & Delorme sent a new USB cable. Sounds like you'll need a few spares on standby.
There's also a longer lasting rechargable Delorme battery you can get http://www.rechargeable-lithium-batt...om/cabbat.html
Consider anti-corrosion treatments such as http://www.aircraftspruce.com/catalog/cspages/dc4.php
or ACF-50. Double check ACF50 can be used on electrical; I'm 90% sure - just right for 'interweb' advice.