All fuel dose deteriorate when stored. Filling the tank and a dose of stabiliser/anti fungal is the way to go.

Bugs and moisture are you biggest enemy with fuel. Moisture from the atmosphere will get in what ever you do, Aviation fuel stored in 200ltr drums must be laid on their sides and have the bungs positioned at 3 and 9 o'clock so that they are isolated from the air gap in the drum by the fuel itself. This prevents moisture being drawn in past the seals by the change in atmospheric pressure as temperature and humidity levels rise and fall.

One other thing to consider is the time of the year that you store fuel as it is provided as either a summer mix or a winter mix.

Lou...