Only down side to this is condensation build up and reduced evaporation due to reduced air movement.
Say it's been soaked through, you then park it in the sun for a day, the water cannot exit the chassis except down the way which is not conducive to evaporation.
If the chassis, bulkhead, door pillars, door frames have been blasted with the correct grade of Dinitrol, then you want it to do it's job by being a barrier and you want normal drying processes to allow the chassis to dry out naturally.
Dinitrol - bearing in mind that is just the brand and there are about 10 versions, of which one is a very thin substance which is used at the factory by some big name car manufacturers like BMW and VW which is a penetrating fluid which will go like a vapour when sprayed, run everywhere and leave everything it touches with a waxy coating on it which is what I used internally, you can spray that stuff in the bottom of the door pillar and it will mist out the bulkhead about 2 feet away.
I do know of one guy who filled his chassis of his restored bus with about 50% by volume with oil, he put in drain plugs, and filled about every other hole in the chassis, every year he would dump the oil and refill it. I wouldn't much like to use used engine oil as the heavy metals, acids and hydrocarbons could actually erode the steel. But he liked it.
I drilled every 6-8 inches on the chassis and plugs mean I can pop em and redo with ease ..... 
