I think i do what you want to know, at least i think it is....
Check out the coimic to be sure Lun
I draw these in a vertivcal a5 paper, scan them and than photoshop them around a bit.. I save them as 640x940px - 100 dpi.
(The next step you can do different but i do it this way)
Open illustrator set up a 640x4000px, do the montage, put in the lines to separate the frames. and since illustrator cant the save artboard in jpg, I save it in pdf and than run it through Photoshop to actualy save it as jpg (Tapastic doesn't accept pdf).
I usually fit 3 frames pet jpeg ( 4000px height is the max that tapastic accepts) it usually ends up on the 5-8 jpeg's, so just select them all when uploading.
I can give a more detailed explanation if you need it.
If it is story wise than I dunno just storyboard it with the longer form in mind.
And if you want it to make it just a long seamless thing, well you can just elongate the artboard on your software of choice. or just draw it as a whole and than cut it by frames.