In the current issue of "Land Rover Owner International" magazine, there is an advert for a product called "KLEENtect"
There is a testemaonial for the product from a gentleman who drives from Colonsay to the mainland when the tide is out. He claims that after using this product and driving through salt water for 7 months his landys underside is still perfect.
Their contact is 01635 32068 or www.before-n-after.co.uk
I have no link to this product and have not used it myself, but I have read positive comments about it. Just thought you might like to know that there is an alternative to wax oil.