What are the chances of securing permission from the actual owners?

Rural neighbors notice strangers and exchange phone numbers.
For just this sort of thing.
And.
Someone pays the utility bills.
Any change in water, electricity, or propane will trigger an investigation.

If caught, expect to be way, way under the bus.
They will file a civil suit on you to cover their ass and prevent property seizure.
And probably lay trespass charges as well just because it supports the suit.

But the main reason I would advise against it is ethical.
Ethically, it is wrong.
Do unto others . . .

Now, if the owners agree to your plan, and share in the harvest, that's a different animal entirely.
Go forth, and grow heartily.

Aloha,
Weezard