[SimonP]

Craig,
You shouldn't need anything else, provided that:

1. You only fill the tank half full, when the engine is cold.

2. The UNDERSIDE of the top hose at NO POINT is EVER higher than the coolant level in the tank.

Example, if you have a stat housing with 45 degree upward outlet, then you use hose bends etc to bring this back down to your header tank inlet, you will have problems because the water pump doesn't have enough "oomph" to push water over it at idle. - Hence the water in the engine will start to boil, pressure will increase and some will be blown out the pressure relief outlet.

As long as your top hose remains about a quarter full of water at all times, you should not have problems.

If this looks OK, verify the engine temp and radiator inlet and output temp with an infra-red thermometer, as the dash gauge will likely be inaccurate (mine reads about 98 when the real temp is 87).
If the rad inlet temp is a lot lower than the engine temp (on stat housing) then coolant is NOT CIRCULATING properly.

Note - if you have a chromed stat housing, you will have to temporarily apply some matt black paint or insulation tape to it, in order for the IR thermometer to give a true reading.

If this all still looks OK, it may be worth having the system pressure tested - a minor head gasket leak can cause coolant to be forced out due to system over-pressure. The leak can be so small as to let gases into the coolant, but not allow coolant into the cylinders.
They should also be able to test for the presence of combustion gases in the coolant.

But, first things first, make sure the system can flow properly.

Simon.