P219 CEEFAX 219 Tue 26 Dec 21:42/42    While most families are gathered together in the comforj of warm homes on Christmas Day, one family - the Seegers - will be celebrating on the top of Ben Nevis. What makes Alan4 Penny and their 12-and 13-year-old daughters want to spend the Christmas season on top of Britain's highest mountain? They are testing camping equipment to be used on a new type of adventure holiday on which tourists will carry their own equipment and rough it in guch places as the HUmalayas and the Andes.