Hi,
Yes, mojoPortal does work in Medium Trust. If you search this site for "GoDaddy" you will find a bunch of people are using mojoPortal on GoDaddy and they enforce Medium Trust. I test Medium Trust on a regular basis to make sure it works.
I recommend review that page again and make sure you have followed all the steps carefully, don't second guess or skip anything, recycle the app to make sure it takes new settings.
Other than that, its possible that you are not running in Medium Trsut but some custom trust level as some hosts use a modified Medium Trust.
Hope it helps,
Joe