Op is the cracking in the actual paint of your rig or it sounds more like it might be in attached decals which will crack over time. Wax won't help with cracking or fading from the sun. Before I got an RV I had a boat that the top trim line all around it was black. I tried everything to keep the black as shiny as the rest of the boat sitting in the sun at the marina and reflecting water, including various types of black shoe polishes. Best thing to use is 303 Protectant. It has UV protection, is easy to apply which is basically spray on and wipe off which makes it quick to keep up the protection and shine throughout the season. Camping World will occasionally have it on sale for around $58.99 a gallon but you can probably find it cheaper online. I bought a gallon on Amazon last summer for $48 or so. Good luck.
