Calculate the volume, capacity, mass of fuel, and total weight for a rectangular tank with given dimensions and fuel density.

Length ($L$) = $8 \text{ m}$
Width ($W$) = $5 \text{ m}$
Height ($H$) = $2 \text{ m}$

The volume of the tank is $\boxed{\text{80 m}^3}$.

The capacity of the tank is $\boxed{\text{80000 L}}$.

Density of petrol ($\rho$) = $8.8 \text{ kg/m}^3$
Volume of tank ($V$) = $80 \text{ m}^3$ (from part a)

The mass of the fuel in the tank when full is $\boxed{\text{704 kg}}$.

Weight of the tank ($W_{tank}$) = $500 \text{ N}$
Mass of fuel ($m_{fuel}$) = $704 \text{ kg}$ (from part c)
Assume acceleration due to gravity ($g$) = $9.81 \text{ m/s}^2$.

The total weight needed to be supported is $\boxed{\text{7406.24 N}}$.

Total weight ($W_{total}$) = $7406.24 \text{ N}$ (from part d)
Number of supports = 4
Diameter of each support ($d$) = $32 \text{ mm} = 0.032 \text{ m}$

Radius ($r$) = $\frac{d}{2} = \frac{0.032 \text{ m}}{2} = 0.016 \text{ m}$

The tensile stress of the steel support is approximately $\boxed{\text{2.30 MPa}}$.