Guys,
For undercoating, dont spend unncessary money.... Just go to Wurth Lanka - Nawala. or to nearest lube shop.. Wurth has good undercoating products and its from germany. I have used a product called "High Build under seal". its a aerosol spray can and costs less than 2000/-. You ca do it yourself. But the vehicles underbody should be cleaned and dry.
And they have a another product which needs some tools to oparate. Choice is yours.
Dont know whether i went too far to promote this product, but i guess its a good thing to promote good, cost efficient products.
I heard clean park's tuff-kote also good on this but expensive.