So are you printing at exactly 48 x 96 and expecting to get no white?
Most panels are slightly wider or longer than 48 x 96... And a lot of times not perfectly square.
I would start adding a 1/8" White all around the image if possible...then just put on your vinyl, use a straight edge and cut the strip off.
Or... if you have the space, spend the $250 and buy one of these -
https://www.ebay.com/itm/263276395115?hash=item3d4c7efa6b:g:8WAAAOSw2xhh59o5 . Mount it between 2 tables and applying 4x8s will be a breeze and take seconds.