Once you've added bones, the mesh will already have some kind of weighted solution but it probably will be far from perfect, and we'll examine what needs attention and fix it. Work from the larger issues to the smaller ones, and just work down one side of the mesh. It's not time to start animating or moving the rig around just yet though. First, expand the Advanced Parameters section of the Skin modifier parameters.
The main thing to change here is the Bone Affect Limit value. Few parts of a real body would be significantly influenced by more than four joints, let alone 20. For performance purposes too, the more bones you allow to affect a vertex, the more intense the calculation. Some game engines limit this internally, so it's best to skin with that in mind so the solution in 3ds Max isn't broken once you export for gameplay.
Under the Bone Affect Limit value you'll also notice a section where you can Save to file and Load from file your Skin solution, using the...