Thanks for the suggestion spuluka. Running the Junos from a USB stick would give me enough space to install and run JWeb. However, I have been unable to get a "request system snaphsot media external" command to complete successfully. The command succesfully partitions the USB drive, but somewhere along the process of copying file over to the USB, I start seeing errors. The system then seems to freeze and reboots. I typically see the following message in the console before things freeze and the box reboots:
umass1: BBB reset failed, TIMEOUT umass1: BBB bulk-in clear stall failed, TIMEOUT umass1: BBB bulk-out clear stall failed, TIMEOUT
I have tried different versions of the Junos software, and three different USB drives. All fail with the same symptoms. I seem to be able to read files from a USB drive and install Junos versions from an USB drive. I'm guessing that I might have a bad USB port at this stage. For now I have reverted to Junos 12.3 as it has a fully featured JWeb interface on install.
Thanks again spuluka for your suggestions.