I plugged in some numbers, and got 0.000622", the variation might be in the E(i used 30,000,000) and I(i calculated 132.4in^4). (assuming 12x4 rectangular tube with 1/4"wall, the 12" is vertical)
To take into account beam weight, its cross section is 7.75in^2, density is 0.284Lbs/cu.in, its weight is 2.2Lbs/in.
Now go into the uniform loading calculator, it says 0 deflection, i calculate it on my own, its 0.0000042"
I'm pretty sure these deflections can be added (please verify), but deflection due to beam weight is so small it can be negated.