i spray a little expandable foam in the shell,just be carfull not to put to much. i usually fill the cavitity a quarter up.i rig my bars with a bead in front of the crimp so i can pull the shell tight so no foam comes out the top.
Dish soap is the ticket because it eventually dissolves away. WD,oils, Vaseline, etc. will stay in and on the squid, line , etc. and if petroleum is left on stored line for extended periods of time it starts to degrade and stain it.
I use backer rod (caulk backer foam) as floats. Works great, can cut it to any lenth you need and comes in different sizes to fit in most any squid. I use spit to lube it. You can get it at most any hardware store cheap.
With the light foam backer rod inserts my squids seem to float higher and drag less.
Soap is the ticket, I typically use canyon runner floats but have used the foam from reel draggin tackle, the foam floats from CR last longer but both work well. The floats might be a tight fit if the squids are cheaper sea striker brand, they are a thinner body then most squid and taper a bit making them tougher to rig, but the floats do fit, just need a little soap to pass them through. A rigging beed and crimp at the end nelp pass them through easier and need to be done regardless so that might help you out. Good luck!!