As soon as you give any client access to your sketchup file for viewing purposes, via Trimble Connect or any other means, they will always be able to download and edit that file.
I would like to be able to send models to my clients in a way that they cannot edit them.
The only way I see this happen as it should would be to have a specific file format variant for a sketchup model that could only be used for viewing/reference purposes and would be locked from edition in Sketchup.
They could open them in Trimble Connect, Sketchup, Sketchup for iPad, Sketchup Web, or any compatible software for viewing purposes, but they wouldn’t be able to edit them.
You could open it or insert it as a component in a model but you couldn’t edit the model or the component inside another model.
You shouldn’t also be able to convert it into a different format.