If there is one problem that Sketchup has as a truly viable software package it's that you have to find work-arounds for it's buggy weirdness. For more complex models using spline cages etc. I use MODO for it's brilliant sub-d integration, relatively low cost (compared to other "big" packages), and it has the best interface of any advanced 3D package. But that's a different discussion...
-If you can't "see" your geometry or things disappear, it's probably because the scale of the model is small and so when you try to do certain operations SU just makes the really small pieces disappear as if being unrecognizable. The easiest way to deal with the small geometry SU problem is to use the "boolean helper" plugin which really only does two things: it scales up and it scales back down again. Of course you can do this manually, but it's nice to have easy to use buttons that just do it for you.
-To get around camera clipping turn your perspective on (which will unset the clipping), then do a couple of operations, then turn perspective off again (if you don't like perspective on). I always have to do this periodically.
So without being able to see what your model is specifically, here is what I would recommend:
It sounds like you trying to build spline cages for skinning. For this type of operation SU isn't ideal, especially for complex models, but you can do it. First, don't try to skin the whole model in one go. Do it in pieces. In fact I would take pieces of the model and copy them into separate files, then after getting each piece to work, copy and paste the whole model and put it together. - I think SU gets confused when dealing with large groups of complex geometry and performing operations that it's not necessarily good at, but it seems to do better when dealing with smaller compact units and them putting them together. By separating these pieces you might also find where the real problems are.
