A William Claridge, aged 19, arrived in Australia 19 July 1848 on the Royal Saxon, origin Banbury, Oxfordshire, on an Assisted Immigrant passenger lists (info from ancestry.com). Oxfordshire is a neighbour county to Gloucestershire where William may have been from, so it is possible he travelled from Banbury. I can't find a ship's list for the specific 1848 voyage. There is a return list from Sydney to Calcutta 31 Aug 1848 on the Royal Saxon, but the incoming list doesn't seem to be transcribed online yet (perhaps I didn't look in the right places!). If you can find the specific list or even a newspaper entry that listed the arrivals, you may find out if this is your William or not.
There is also a convict William Claridge of Somersetshire, sentenced May 1841 and arrived 1842. I have no idea if he was close to the age of the William you are looking for.
I assume you have the info on Mary Ann's death in 1891, birth of son William North in 1857 at Port Sorell, and will of William in 1896? There is more on the descendants of William North Claridge online, but I assume you found all that.
I found no other helpful info for you on the Tasmanian Pioneer Index 1803-1899 or on ancestry.com.