Had a reply from the sis-in-law already, bless her.
Apparently Port Solent would be favourite, thats J12 off the M27. It has acres of
free parking, whereas Gunwharf costs a fortune to park, and several eateries including a pub, The Mermaid, which does a fair meal. Ten minutes from the port by car so handily placed too. There are some convenient hotels too for anybody who wants/needs somewhere to rest up at all en-route.
Almost as an afterthought she suggested this place, The Sovereigns,
http://www.pub-explorer.com/hampshire/pub/sovereignsportsmouth.htm located just off the M275 into Portsmouth, right opposite the Ferry Terminal. Parking, pub grub and accommodation all in one place.
Over to you guys.