Sure it can be a PITA but it works if you seal well.
IF I need a taller bag I first measure the length I will need , cut it then split it down the side to make one wide flat piece of plastic. Then take another piece the same length and cut it down the side. Then take the two separate bags and seal then together twice (I like to double seal). then fold it over and seal the other side. Finally seal the bottom of one end put your stuf in and seal the other end.
I will draw a tutorial BRB