Thanks Nick, makes sense.
Finally got the whole thing working on GSM/GPRS. I've removed camera option for now to reduce data upload time. I also uninstalled Weewx and write directly to WU with "GET" command. This greatly improved Zero performance. The station now cycles measurements every second again. It stops every 5 minutes, turns on "PPP" connection on Fona, uploads data, then turns off the "PPP" connection. I discovered running the PPP crashes the I2C BMP180, hence the stop to upload. The "PPP" is only connected for 20 seconds so power usage is low.
Power usage seems very good, 70mA on Zero, less on Fona (it has a 1000mA LiPo)!! I'm thinking of the Sparkfun Lipo / solar setup if possible rather than a 12v lead/acid if I can. Any experienceof these?
I've attached a picture of the setup so far. [ You are not allowed to view attachments ]