I use a Lee melting pot, a 6" Cast Iron Frying Pan, a bungee for the strap, 1/4" acrlic plastic for the fin and a couple 1/4" bolts to hold it all together.
I use the brass strip to measure the depth/weight.
Cut a slot to fit the bungee strap 1'' below the centerline & run the bolt thru it all.
Use a file to smooth it all up, Paint & add reflective tape!!