Success, and with minimal ballast....

[DustyRusty]

When I was involved with construction, the standard rule of thumb was that it took 30 days for concrete to fully cure. That was 60 years ago, so things might have changed since then. .

 

[eipo]

For 400 pounds, you wont need any ballast so the box filled with stone will be fine.

ETA: Response to Orange man

 

[Mrlunchbox]

I bought the Kubota box that goes on the back and intent to fill it with 60lb bags of gravel. IT will take at least 4 bags maybe 6. Is that enough weight. I probably won't life more than a few hundred pounds, maybe once in a great while 400.

That's what I did with my 1880. Got a used Kubota box, filled it via bags of river stone to get to the correct weight. Been good so far!

 

[Russell King]

When I was involved with construction, the standard rule of thumb was that it took 30 days for concrete to fully cure. That was 60 years ago, so things might have changed since then. .

There are different uses of the word “cure”.
It gets hard in a few hours so is it cured?
It reaches maximum strength in about 30 days so then it is cured?
I think it just depends on what level you are interested in.

 

[Orange man hero]

That's what I did with my 1880. Got a used Kubota box, filled it via bags of river stone to get to the correct weight. Been good so far!

Sounds good....Tnk...