What is the best place to put a landclass file? Would it be in the scenery/base/scenery folder? Or the addon scenery/scenery folder? Thanks :)

A separate Scenery folder called Landclass, for example, under the Main FS Scenery Folder. Note that there should not be a Texture folder, since that can cause strange effects. Note further, that this is a general rule and the individual designer's suggestion should trump this rule if his instructioins so state.