Version 1.6 onwards of FulGaz will work completely offline if you do a bit of preparation first. Here’s how you do it.
Download the video. Either directly to your iPad or if you have a slow internet connection, to a computer first from here.
In a place where you have an internet connection, start viewing the ride until the elevation profile appears at the top of the screen. This downloads the ride profile and GPS data and saves it within FulGaz for further use. You don’t need to be riding to do this.
Repeat this for as many rides as you want and you can then ride them without the internet at all.
It is worth noting that FulGaz will let you do a ride offline but it will struggle if it is disconnected from the internet for days or weeks on end. Whenever it is turned on it looks for new rides and tries to send your ride data (if you’ve asked it to). Eventually it will start to complain and eventually it will refuse to work because it can’t “talk to base”