One of my buds quit bass fishing and gave me several hundred tubes and Yamamoto grubs as well as 25 packs of brush hogs.  I won't need to make any baits for a year or more.

Is turning the plastisol bottles upside down and right side up every once in a while enough to keep it ready for use or is there something else I need to do?  

I'd hate to have a couple of gallons go bad while I don't use it.

I dont think it will go bad from just sitting there.  Just make sure you stirr the crap out of it before you heat it up.  It will settle and the parts will seperate from just sitting there, but stirring it and shaking the bottle if it is a one gallon bottle should work.  

It will be fine. Just mix thoroughly before use.