how to use an Exsisting Visualforce page in a Tab set

Is it possible to add an existing VF page to a tab in Skuid

Yes!  It is generally possible.  Start here:  https://community.skuidify.com/skuid/topics/visualforce_missing_as_option_on_page_include_component

Here is the iframe syntax i am using

Hi,

you do not need to indicate the first part of the link , try this instead