How feasible is it to convert a 30-35ft boat somewhere around 6-9 tons displacement and rig it as a sloop? Would a rig of 600-700sqft require too much steering force for windvane self steering? I understand a ketch or schooner rig would be preferable,  but the simplicity of a single sail is appealing. 

The only example I've found is Paragrine, and I'm unsure is she is used for long range cruising much.