Join Date: May 2005
Location: Mayenne France
My Motorhome: Pilote 733 FJ
Thanked 185 Times in 162 Posts
The problem with lubrication based coverings (oil, grease) is, that whilst they may be partly effective whilst they are in place they will wash off, in the days of spraying old engine oil etc. it was accepted that it needed doing at least annually.
Paint based ideas are better but the surface to be coated needs to be clean and dry and ensuring full coverage is difficult.
A better bet would be one of the purpose made products, be they wax based or bitumen
Depends on which part of the underbody you're trying to protect, is it the vehicle base chassis components, or the converters parts, floor panels etc.
Most recent van base manufacturers have the chassis parts protected well and if the van is old enough for that to not be the case then it's probably too late to worry about protection.
That leaves the floor and exposed lower parts or the conversion, just make sure whatever you choose to use the areas to be covered are thoroughly dry and clean.