So don't go crazy if you guys already had a solution to this problem.

As most tutorials suggest is that one uses HMT v3.5
to extract a model put it in Misfit Model 3D edit it a bit and import it back in to HMT v3.5
There are some people that have trouble with .OBJ files and importing it to Misfit Model 3D.
For example me:

As you can see in the images, I have the correct model of the masterchief in HMT v3.5 and imported it in to Misfit Model 3D. The result no masterchief in Misfit Model 3D.
I did some research on the Internet, as most people do when they encounter problems, and it seemed that there were more people with this exact same problem, but no solution.
So I contacted one of the admins at Misfit Model 3D gave him my model of the masterchief. He had a look at it and found out what the problem was.
"floating point was
expecting period, file contents using comma; presumably due to being
written with a non-American localization"
Meaning that instead of using dots like the Americans do, my European OS used comma's.
Example USA: 5,000,000.99 Example EU: 5.000.000,99
This problem has been fixed and it will be released in version 1.3.8 of Misfit Model 3D.
But there is more, I also found out that HMT v3.5 only accepts floating points written with an American localization.
Meaning that if I, with my European OS, export a model and try to import it back using the exact same model without changing anything at all, that HMT v3.5 would accept it, but you would end up with no model or just 2 lines or so in HMT v3.5.
So it was back to the lab again, mailed the admins at Misfit Model 3D.
Gave them my model and the one of a US friend of the shotgun.
Exact same problem, so I requested to add a "save as" option or a converting option to Misfit Model 3D, that will allow people with this problem to save the files as if it was written with an American localization.
I got an email back that it will take a few days, but they will add it.
So for anyone who has this problem, just wait a week or so for the new version of Misfit Model 3D.
Hope it helps