Hi Dunns2
Sorry but can't think of an easy place to park near the ferry terminal but I'm sure there should be somewhere close - Southsea promenade springs to mind!
You're welcome to stop outside my place overnight but I'm a 40min drive from Portsmouth so still a very early morning. Phone the port authority and ask them for suggestions.
One thing you do need to watch is the date. The Trafalgar 200 year celebrations and festival of the sea are on in Portsmouth this year and I think it is July sometime. Portsmouth will be heaving during this time so check it out.
Gaspode