Zeke, you read my mind on this one.
I have been thinking about doing this too, and will follow this with some interest.
I was thinking of adding some webbing for handles, maybe go all the way around the case for strength, and pop rivet through it on the side opposite the handle. Put the padding in after that to cover the rivet heads and backup washers.
For a lining I was thinking of rolling some insulite, like a sleeping pad, and cut to a tight internal fit after putting a round piece into the ends. Dry fit it real close, then take it out and use 3M spray adhesive and put it back in. But I think I would still want to wrap the bow pieces in a bow sock or something, and put the arrows in a box before putting them inside so they aren't rattling around.
Another idea for padding; there is a product used here a lot as insulation in commercial fishing boats that comes in a 4' wide roll, I can buy it by the linear foot. Here it is called ice blanket, and it is a closed cell foam about a half inch thick and is white. I might use that instead of the insulite since it is handy. I bet you can find it if you are near any fishing port in California.
I might see how much room I have and put two layers of padding if I can?
I made a case like this for rolled maps (without the padding) to use on float trips using 4" pvc and it worked well, but I found that the screw end leaked a little water if it was immersed, unless I coated the threads with silicone paste. Mention this just in case you are going to be in sloppy situations with this. I am in open boats in the rain a lot.
I was thinking of using a second piece of pvc for the arrows if needed and riveting it alongside the first piece, and backing the rivets up with stainless hose clamps around both tubes, but if one bigger piece would hold both, that is better and simpler. Of course you could just make two cases, but if you are going to check them on an airline, it would be better if they were one item than two.
Those are my thoughts on this project so far. I was just waiting for things to gel a bit in my head, and looking to get hold of a big piece of pvc scrap before I tried it. Look forward to any better ideas.
Walt