If you want them to be able to turn around then you may need…
Yeh, I know… time for a taxi… 
Just employ them lads who guide you on the boats… they’ll get more trucks in per acre than anyone else! They can pack em in like sardines!
If you want to know about spaces required look at any dockyard and see what way the dropped trailers are configured for max space and accesibility… just add the necessary dimensions of a tractor unit.
A warden to assist you to back you in would make sure space is not wasted by pricks in 7.5 tonners and supermarket so-called drivers needing three spaces to park up would be a good idea.
One acre is equal to the following customary units:
66 feet × 660 feet (43,560 square feet)
1 chain × 10 chains (1 chain = 66 feet = 22 yards = 4 rods = 100 links)
100 links × 1,000 links = 100,000 square links
1 acre is approximately 208.71 feet × 208.71 feet (a square)
4,840 square yards
160 perches. A perch is equal to a square rod (1 square rod is 0.00625 acre)
10 square chains
4 roods
A chain by a furlong (chain 22 yards, furlong 220 yards)
0.0015625 square mile (1 square mile is equal to 640 acres)
So:
If you have two rows of trucks facing each other you would need a plot about three truck lengths wide plus a bit - Say 180 feet. So if the plot is 180 feet wide then it would be 242 feet long. I would have thought that 10 foot bays would be wide enough so there would be 24 on each side and 48 in total.
This assumes that all the spaces were useable even the blindside ones at the end.