is this a 26 or 700c wheel? 36 spokes or more?

Rhyno is a good rim and normaly should give you good service. If the cracking is on the drive side the spokes may be over tensioned. because of the dish of the wheel the drive side has to carry more tension The spokes these days are so well machined and are strong enough that it isn't difficult to over tension them to the point where the rim fails before the spoke.

If you are getting a new rim from Sun at Hermosillo and assuming this is a 26" wheel you might consider a Sun Mammoth it weighs about 150 grams more and is about 2 mm wider. more importantly it is thicker around the spoke hole and should handle stress a little better. It also has the advantage of a smaller ERD which makes getting the tire off the rim much easier than the Rhyno. If you end up with a new hub also go for 40 holes if you can, You certainly should not be using IMO a 32 hole or less wheel.

some might reccomend using a 4 cross spoke lacing pattern, I would avoid that . Small flange rear hubs with 4 cross spokes tend to have problems because the first cross of the spoke is too close to the hub

Rick