According to the online help for the Post (which the CS manages), when you place the userDefined variables into your submission template you call them out by type:

userDefined1.form.yesNo
userDefined1.form.textarea
userDefined1.form.htmlarea
userDefined1.form.float
userDefined1.form

and so on for userDefined2

There is a maximum of 5 userDefined fields.