The 20amp fuse should be ok. The size wire should be 12 AWG with a 20amp fuse max. If you decide to use a 25amp fuse, you should increase the wire size to 10 AWG (which a 30amp fuse would be ok as well). Don't forget to ensure that the wire between the switch and the power strip or fuse panel is of adequate size as well.
To ensure the 20amp fuse is adequate, just try it quickly. You're only risk is that the wire is two small and it will begin to act like a fuse and heat up... eventually to burn up.... that would be a BAD thing!! So just try it for a few seconds. If the 20amp fuse works... great, then verify you've got at least 12 AWG wire (14 AWG is too small) and you are good to go. If the fuse blows, go to a 25 or 30 amp fuse and 10 AWG wire.
Hope this helps....