I agree with Legacy. My Okuma Convector 30D holds more than 1000 ft of wire, and the line counter will be off if the wire isn't close to the top of the spool. I think I got like 100ft of 30 # braid on it. I wouldn't use anything that is too cushiony as the backing. If it stretches or it digs deeper, then it throws the wire off the line guide and being out of sink reeks havoc, including wire tangles which are not fun when a fish hits.
One thing for sure, when you are out there, it is wise to take a popped open dipsey with nothing on it, put it on the end of the wire, and release as much as possible, one rod at a time, then reel everthing back in. It helps get the wire on right, tight and takes care of line twist.