So here it is, all finished and with some jumpers in it so you can see what it's like. shape-wise. The top is curved, which made it even more fiddly to sew.
It is fully lined with some strong calico and stiffened all over with interfacing. I am hoping all my triple stitching will mean its nice and strong too. I also added some pockets, this fully lined one extends over the front of the bag and will be perfect for putting travel documents and a book or magazine in so i can grab hold of them without rummaging. The end pockets are also lined, with both calico and more oilskin and I think they will be perfect for popping in a water bottle.
I made the bag almost exactly the the airline specifications for hand luggage sizes. I should definitely be able to fit everything in. Now all I need to do is make the shoulder strap (one of those padded ones with velcro) and a wash bag. I need to get hold of some more oilskin for that though so it will have to wait!