The full tank shall weigh 10kN. 995kg×9.806m/s2 plus some plastic.
To determine a load distribution on the beams, we must make some assumption, because a perfectly stiff tank would have just three contact points with the metal, unrealistic.
A uniform load on beams ABCD is reasonable from a deformable tank bottom, without justifying further. But I suppose the construction must withstand a slightly eccentric tank that relies on ABC only. Then if the tank survives, C feels 10kN/3 + 10kN/3/2 = 5kN, not the 3.3kN on C and B and 1.7kN on A and D if the tank is centred.
You can compute the bending moment on C: it's FX/2 if F+F is the length and X+X the distributed force.
You can compute what bending moment the beam withstands: it's σ(H4-h4)/H where H=50mm and h=50-2-2=46mm. S235 steel guarantees σ=235MPa proof stress.
I recommend to compute all in SI units. People using mm, daN and hbar get very annoyed when computing less usual behaviours, for vibrations, shocks, forces by fluids and so on.
Then you can compare both. I'd want a safety factor >=2 if the only possible loss is money, but here with shocks, I'd prefer much more.
You must also check the beam E (F is the same). It feels 2.5kN at 1/3 length from beam C and 1.7kN at 2/3 length from beam B. I expect a stronger bending moment on E than C. Or if the tank is round enough that it relies only on B and C, the E feels 2.5kN at 1/3 an 2/3 length.