In the last five months I have had three Storm balls crack completely around the ball while resting in a climate controlled environment and rotated every month..  I tried to find if there was any similarities like the same coverstock, all symmetrical vs. asymmetrical, solids vs. hybirds vs. pearls, same cores, or that the balls came from the same line e.g. Premier, Master, Thunder, etc. that the balls might have shared, I could not find any similarities other than all three were produced from 2012-2014 time period.
Lost the IQ Tour Edition Solid, Firestorm Pearl, and Crux Hybird.  I'm going to Staples tomorrow and buy some clears plastic bags for small desk wastepaper cans and put all my many remaining balls in plastic to see if that stops what has occurred.  It's worth a try as you all know how expensive these balls are. 

Sorry to hear about so much cracking.
I've been lucky so far, I guess. I keep mine in 2 places in the house, if it helps anyone:
1. In my office, on the first floor, heated and A/C'd in the living area. They're in my bag, sitting in the corner, and on a small rack on ball cups.
2. All the ones not in current rotation, drilled and undrilled, sit either in their original plastic bag in the original box on a handmade wooden shelf in the basement or on ball cups on the same wooden shelves. The basement (well insulated with dehumidifier running during the summer) remains around 50-60% humidity and 59 - 65 degrees Fahrenheit all year round.

CoorZero
Sorry to hear you had similar experiences with Roto Grip as I had with Storm.  As much as my Storm balls have cracked, I have a Roto Grip Rising Star that I no longer use, sitting in my HOT garage (non-climate controlled, as I live in Florida) for the last two years and it is perfectly fine.  It was manufactured in 2011.  Ain't that a fine how do you do!

I too have had issues with RG equipment cracking. I have thrown nothing but RG since 2005 and have probably had upwards of 10-15 balls crack. It is really frustrating when you spend this kind of $ on equipment and have it only last a few years before cracking. I have never lost a ball to Ball Death, only cracking. And yes I keep them cleaned regularly and keep them in the house when not in use....Let us know if the bag works...

I've been saying for years to put unused balls in plastic bags.  All of the balls I had that cracked were not in plastic bags.  Out of all the ones in plastic bags, drilled or undrilled, so far, knock on wood, none have cracked.  All of mine are stored indoors.

I've only had 1 ball that's ever cracked. I've had Storm poured, 900 global poured, EBI poured, Brunswick poured.

My only ball that cracked was my first ball a Tropical Storm but I wasn't even using it and it got exposed to some heat in a garage

Mine all cracked in different places. Loco solid started at the top of the pin and wrapped around the pin into my track and to the bottom of my fingers. Ball fully cracked out after I spotted the initial crack within 6 games to the point the ball was deteriorating so badly, chunks of the ball was pushing into my finger grips and I could not get my fingers all the way in.

IQ Tour Nano started as a bridge crack and eventually cracked out and around both of my fingers. Took about a month for it to fully crack.

Zero Gravity cracked around my thumb. I had the mass bias drilled in my track and the first crack I saw was a hairline fracture extending from my thumb to the mass bias indicator. About 2 weeks later, full crack out and thumb was loose in the ball.

But, my Optimus Solid, original Optimus, Menace, Haywire, and other Storm/Roto stuff has been fine. I don't know if it is a recent deal, but it sucks regardless.

I've owned 10 Motiv balls (nothing newer than the Primal Rage) and except for the Rage, no cracking. The Rage problem wasn't actually a crack, but the imbedded logo starting to separate from the regular cover. Motiv sent me a new Rage, and I haven't had any issues with the new one over the past year.