Cling will not be able to cling onto the HDPE plastic tank so will leak around the cling / tank interface. thus a couple of layers and the need to put the cap back on tight.
Some plastic bags will also work but most are too hard & will crease so provide a path for the fuel to leak out of .
Don't know how long it will last for but I have found cling wrap in fuel tanks and I have had mowers up for a week or so .
Good luck
Whle it is up in the air with no weight on the steering, give the front end a grease the steering pins are best greased like this