should be no problem righting with that Murrays bucket, make sure you practice with it b-4 using. there not always just unpack and use, You will need to adjust it your your boat and you. if the bag hits that water before the boat is up it defeats its purpose.
I think as long as your mast is sealed, you would probably be able to right the 18 with the bag, but the only proven solo aid I know of is the Soloright, which is a pole system you walk out on. Practice with whatever you get to ensure it works before you need it.