Hi there,
Welcome to the forum.
Sorry for the delayed reply.
When setting up the wifi on the robot I skip over setting up the internet connection, and just plug an ethernet cable into the Pi whenever I need to update its software.
For getting mobile internet onto the robot I think that the most straightforward option might be to use another WiFi dongle, although you'll need a USB hub or the Model B+ for that, and power may be a bit of an issue. I have also been looking at the possibility of having the WiFi dongle act both as a WiFi client and as an access point (as discussed
here) but I haven't had time to look at this in detail. Very interested to hear about anything you find out on the topic.
Getting tornado to serve via https could be a good thing to do in the future. Although the camera images are served by a separate program which would need to be converted to https as well. At the moment, because I don't have much time (or much of the required expertise) to focus on the networking it's probably best if I leave it as http so that I don't give anyone a false sense of security.
Regards
Alan