Skorpion tank is blow moulded plastic job, so no point in POR15 etc.
If the bikes off the road for the winter, drain the tank and carbies, put some 2stroke oil in and slosh it about to coat the inside of the tank.
Infrequent use of the bike, say within 6 week intervals, Wynn's 'Dry Fuel', Miller's VSPe or Miller's VSP octane booster and a drop of 2 stroke oil at 50:1. All available from Halfrauds, cheaper than online and 'Frost's' in many cases. The 2stroke just helps lubricate the top end on start up after standing idle for any length of time.
Briggs and Stratton fuel stabiliser works as well, just my local supplier 'charges' for the pleasure!
'Super fuel' is not ethanol free, just the cheap crap with some more octane boosters/detergents and some extra stabilisers. If you want real poke, the 'quality' straight pump fuel 50:50 with Avgas is the route and make sure you pay the tax etc and speak to a knowledgable engineer first.
Hope the 'snot' remains banished Steffan.
My regards, Bill.