As Star said very few 48" decks will be 50" or less .
The blades have around 1/2" clearance so you are up to 49" INTERNALLY
Then the 2 sides of 1/4" to 3/16" thick steel adds another 1/2"
Most decks have a rubbing strip on the left side so there is another 1/2" and hey we are now up to 50"
Then there is the chute overhang
I am yet to find a deck other than Swisher where the discharge flap , even when folded fully back does not add at least 1 " to the overall width
So you are now at 51" and if you think you are going to drive in & out with only a 1/4 " each side, you are deluding yourself.
My trailer is 46" between the gates and I have to remove about 1/3 of the 42" decks off to get them in.
Not a single 44 " deck will drive in