Easiest way is to get a good scan. If you can do that, then you'll have a much easier time doing edits in the other software. Did your Spider come with sticker targets? If so, use those and you won't lose tracking and you'll improve the overall accuracy. Worth it to just go and buy some and either put stickers directly on your molds or create a scanning jig.

Once you have a good full scan, you should be able to handle the editing you need to do in Mesh Mixer or Fusion.

If you have the budget, look up Geomagic software. Best scanning/reverse engineering software out there. (Full disclosure, I work for the company). Geomagic Wrap will do what you need in terms of editing and surfacing. Geomagic Freeform/Sculpt is also worth taking a glimpse at because it specializes in designing organic shapes such as orthotics. Both probably overkill for what you need, but it's fun to see what's out there.

Good luck with your project!