plz advise on Water tank

Hi all

I’m planning to custom-make a water tank for my Nissan Patrol GU and the dimensions are as follows:

Length 950 mm
Height 530 mm
Width (Up 200 mm) & (Down 350 mm)

It holds 135 liters and will be placed behind the middle seat.

Please note that it has only one baffle and the baffle’s dimensions are as follows:

Height 450 mm
(Water tank height is 530 mm)
Width 200 mm down & 100 mm up
(water tank width 350 mm down & 200 mm up)
Length 130 mm
(water tanks length 950 mm)
Please note that the length of the baffle is not an important factor,
as far as I know, since it plays no role to reduce the water slopping around.

My mate at the water tank shop told me that the baffle has to be hollow, because he will make the tank from Polyethylene. Since the baffle is hollow, I will lose about 9 liters. That’s why I have to make only one baffle to reduce the amount of liters lost by making the baffles.

So what you guys think about having only one baffle in the above-mentioned tank? Is one baffle enough for my tank to prevent or at least minimize water from slopping around?

Replies are highly appreciated.

Many thanks.