Coating steel with oil will provide rust inhibition. If you plan to off road, you might make a sticky, dirty mess.

There are some products out there designed to do what you want.

 

Instead of gear lube ,use trans oil mixed with kerosene. It will soak deeper in ,is less sticky and will only attract a small amount of dirt. Trans oil is less harmful to wiring than motor oil. 3 parts trans oil to 1part K1.

 

I use the internal frame coating product at Eastwood - Auto Body Repair Tools | MIG Welder | TIG Welder | Plasma Cutter | Auto Body Supplies & Accessories. It comes with a very long tube with a 360 degree nozzle on the end. Two cans per side will really coat it terrific and you should be set. I would think any type of petroleum based product would attract dirt and cause a build up over time. With the Eastwood coating you can flush the frame with pressurized water and keep it clean forever.

 

Oiling with used engine oil was a moonlighting profession for many in the 70's/80's in the Great Lakes States where winter road salt digested steel bodies in less than 5 years.
The practice stopped when it was realized that used oil was acidic ( sulfuric acid is a combustion by-product.) and ate away the sheet metal quicker.
There still are some that undercoat with new oil. Most use commercial products with polymeric formulations that last longer, protect better and add sound dampening.