Have bought an electric swivel towel rail to replace the Truma on fitted in our Bailey Indiana S6.The top fixings look like they will go into a fixing block that old towel rail was screwed to.At the bottom the wall is hollow with a 3mm board the 16mmish gap then another 3mm board.I cant see how to get an umbrella type fixing in.Anyone got any suggestions,the towel rail weighs about 2.5 kg.