Hi Norm, what I do, and has worked well for years is to use a 20 ltr bucket, I have 2 setups incase I need a lot of livies and for when I have both mullet etc and sardines. I keep the 2 seperate. Sardines are fussy
Two 20 ltr buckets fit just nice in the butchers tub I have in the boat.
I made cages out of stainless steel mesh with a solid alum top / lid that fits into the 20 ltr buckets.
The alum top is important as when you hang it over the side in strong current, the bait take shelter against the lid as it hangs in the current.
I have a small bilge pump that sits in the cage with an elbow on it and then a piece of pvc pipe to the top of the cage..another elbow and short length of pvc to provide a sprayer bar across the top of the cage with a cap on the end.
I just drop the pump setup in the cage when I need it.
To make the sprayer outlet I cut a slit in the pvc and then fitted another piece of larger pvc [tapered like a v to cover the slit] over it so I can slide it over the slit to in / de crease the flow rate.
I net bait and drop them straight in the cage [sitting in the water]and then drop the cage into buckets of water in the boat when I'm ready to leave.
If I have to motor for any length of time I pull up every 15 minutes or so and change the water but otherwise I just leave the door in the lid open to allow air in. I mostly fish near where I catch the bait.
When I arrive at the fishing spot I drop the cage/s over the side.
I hardly ever use the pump thing.
I see ppl whack a bit of air tube near the outlet of the pump to use a venturi air feed to put air into the pumped water.
Haven't tried it myself but looks good.
Good luck with the livies, mullet sards whiting and prawns are all I ever use.