Can someone be a bro and take the black plastic rear storage area dimensions under the rear deck?

Most of the problem with retail oil bottles is that they are made to be disposable, so there are problems re-sealing them after first use.

Try a camping fuel bottle. They're commonly used as reserve fuel for motorcycles and camping stoves. The point is that they are made to be re-usable and the seals won't be broken down by petroleum.

 

I didn’t know of the Rotopax fuel storage containers before. They look like quality items.
If I were suicidal I’d try what your suggesting. It is an interesting idea except in traffic. Reminds me of the Ford Pinto gas tank problems from decades ago. Maybe for travel through the desert it’d be a great idea though.

 

History lesson on carrying gasoline improperly
The Ford Pinto - The American Museum of Tort Law

 

I think the OP just wants to carry motor oil in the cabin. While not entirely risk-free, it's got to be a heck of a lot safer than carrying gasoline.

The point of using fuel containers is that they are a lot less likely to have chemical incompatibility/degradation with exposure to oil.

 

Many have stored an upright quart or two in the small cubby near the left tail light, opposite the 12v battery.

 

I'd be skeptical that any gas container permanently stored inside of the vehicle is going to behave. Suspect it's just a matter of time before you get in your car and the interior smells like toxic gas fumes. But, perhaps you could clear out spare tire and storage space above it and weld up an auxiliary tank that is connected to existing fuel delivery system?

 

Want to keep the vapors away from the 12v battery area, just in case something sparks a connection