The project 710K Begins.

[Alaskantinbender]

This dang warning light caused me to carry 2 full Jerry cans

Because when that goes off, I consumed 15 gallons, so I either
press on and hope or turn around and have exactly enough to
get out

That sounds like a problem for sure. I hope not to have the same issue. I had about 13 gallons in my tank. Siphoned out approximately 8 gal, and the light came on. Seems about right, although it's hard to say how much of the remaining fuel is actually usable.

Do you have an idea what the gauge should read with about 5 gal left in the tank?
It would be nice to calibrate the gauge on the low side instead of the high.
I would guess just below the first tick, but really have no idea.

[rmel]

Hard to say. You have a more recent VDO gauge, so you may just have to experiment with it.

[Alaskantinbender]

After transferring fuel back and forth this morning with my electric pump can say that the low fuel light comes on at +/-5 gallons of usable fuel left in the tank. So I adjusted my gauge as close to zero as I could get at 5 gal using the low fuel light.

[Alaskantinbender]

This dang warning light caused me to carry 2 full Jerry cans

Because when that goes off, I consumed 15 gallons, so I either
press on and hope or turn around and have exactly enough to
get out

That actually sounds about right, given it's a 20-gal tank. I had it stuck in my head that it was a 32-gal tank from my Unimog days. (OOPS)
I have calibrated my fuel gauge to read zero at the 5-gallon mark when the light comes on. Yes, it's the same as yours and I will have to add another gas can as well.

[rmel]

I hung my Jerry can holder on the Right side of the read door.

If you put one there, add a steel backing plate on the inside to
prevent weight and vibration from fracturing the thin upper
deck sheet metal.

[Alaskantinbender]

I hung my Jerry can holder on the Right side of the read door.

If you put one there, add a steel backing plate on the inside to
prevent weight and vibration from fracturing the thin upper
deck sheet metal.

Great idea on the backing plate/doubler. I will have to think about which side to put the can. I have seen some with 2 cans on the back, one on either side of the door.