When Sandown Tower is not available, one simply Joins overhead, looks down at ground and check direction of the windsocks, decend over the bay and join crosswind (LH on 05 or RH on 23), while making blind traffic calls, to advise anyone else on the frequency who you are and what your doing.
Its really simple. It really is.
And keep a good lookout as there could be someone non radio.
There are actually numbers in the grass at sandown. Big white ones. One end even has a displaced threshold with a couple of massive pointy white arrows.