Yesterday I found a cheap and eaasy way of doing underbody belly pans with a dimpled surface.
2m x 20m roll costs around 49€ in a DIY hardware and construction materials store, I don't know if it is made in china one or any details (I found at Bricomart
Bricomart France,Italy, Poland and Spain only).
The cheapest coroplast ("policarbonato de doble hoja") that I found was about 20€ 2m x 1 m pieces, gray PVC 3mm 1 m x 2 m 63€ and transparent Polycarbonate of high quality and durability 2 mm pieces of 1.25 m x 2 m at 162€.
Magic words are "lámina drenante".
Magic english word also exists and they are: "drainage layer".
Some links with pictures, data, and garden installation in spanish:
Google search of Lámina Drenante -pictures-
impermeabilizacion « teoria de construcción
TECHMO
http://www.techmo.es/pdf/ft/FT_TECHMO%20LAM%20DREN.pdf
http://www.techmo.es/pdf/ft/FT_TECHM...DREN%20MAX.pdf 320KN/m2 resistance.
http://www.presasl.com/fichas/Drentemper.pdf high resistance 320 to 500 KN/m2
Impermeabilizacion Madrid, Cubiertas, Cubiertas Ecologicas, Cubiertas Fotovoltaicas, Goteras, Humedades, Losas, Filtraciones, Aislamientos
Some links in english:
Pictures of drainage layer Google Search