Hey, thank you for the answer.

The reason why it needs to be a solid is that I'm still going to place some solid volumes on it and then UNION them creating one solid as a whole. Why? I am going to cut it in a CNC router (Ouplan 2015) using dense foam. The 3D printing lab here tells me that the object needs to be a Solid, or watertight, but best if a solid. If I place these new solids on a mesh terrain, then the intersection beneath will create printing problems, as told by the guys from the lab. It's the first time I'm preparing a file for a CNC Router, so I'm taking their words.

Do you have any other idea?