If you hinge the whole assembly so it swings out of the way I can't think of a
problem. The question of working space only requires that there is free access
above and below the panel, from grade to 6' 8" high, 30" wide and 36" deep. If
you had a box with a door it can be argued that the box encroaches above and
below (still a thin beef) but if the whole box swings away you are OK.
Just be sure the meter reader can see the meter and the seal to avoid that
hassle.