The method is as follows :-
It is a puzzle that Alde recommend covering the heater vent when overwintering or long periods of non-use, but provide no means whereby this can be done. Ian has put forward a straightforward solution using a bread bag and elastic band - this is an alternative 'higher tech' solution which you may wish to consider.
1. Buy a small square sandwich box from the pound shop - mine is about 11.5 cm square x 6 cm deep and is marked as 0.6 litre. It is important that the top edge of the base has been rolled over and hence has a smooth top edge.
2. Discard the flat top (or use as a coaster) and check the box fits over the vent with the roll top edge against the caravan
3. Drill two small holes at the centre of the base and about 40mm apart
4. Obtain a 'tie wrap' about 200mm + long and pass through the box, around the centre vent (with the embossed Alde logo) and back through the box
5. Take up the slack in the tie wrap up but do not pull this too tight. This should then hold the box lightly against the caravan
6 When you need to use the gas heater, cut the tie wrap and remove the box.
7. Place a warning notice on the Alde unit to remind you to remove the cover before gas heating is used. SERIOUS DAMAGE WILL OCCUR IF THIS IS LEFT ON WHEN THE GAS SYSTEM TURNED ON!
This looks like a good mod which I think I will give a go at.
One extra suggestion crossed my mind and that is instead of using a non-reusable cable tie you can get reuseable ones ( I've got some ) so getting away from using a new one every time.
Thank you David for your time and effort.