Hi Lin,
A belated welcome to RootsChat.
I'm sorry you have had no reply to your posting. Unfortunately Hampshire is not well served for census information online or on CD until 1871. So there is no index for 1861 census. I can't immediately offer an explanation for them marrying in Portsea, unless Joshua was working there, or was in the marines or something?
Hope you eventually find an answer.
Nell