I tried putting the tube in my seaport or my seat tube but it was too difficult to even get halfway in.

when putting the tube in the bag, it is unboxed and It's a standard tube. With the tube in, I can only fit in a multi-tool and probably some tire levers.

As for getting a bigger seat bag, the next size up was too bulky IMO. I'll fiddle around with it some more and see what I can do.