lower dust boots

[mudflapj16]

  Hey guys. Thanks for all of your help in the past, and now I have another question that I need to ask. I am having a problem with my polyurethane lower ball joint dust boots. I recently put my spindles onto my upper and lower control arms, but left everything loose. I had to have the car on all four wheels so I could weld in my sub-frame connectors. I didn't tighten everything up, because I was kicking around getting 2" dropped spindles. But put the boots on just in case I decided just to keep the stock spindles and just tighten everything up. Anyway, my Charger was only on all four tires for about two weeks and when I was done with the sub-frame connectors, I noticed that the both lower ball joint dust boot covers had a cracks in them (see pic).
  My question is, is this common with polyurethane? Was it my fault because I didn't have everything tighten down? I bought the front-end kit from PST, could it be just a couple of bad dust boot covers? I bought new poly dust covers from energy suspension, but I do not want to put them on if they are going to just crack. Should I use original rubber or how can I keep these from cracking.
Thanks a lot for any help and help in the past.

Bob

[Fred]

My dust boots are rubber. I got them from PST and haven't had any problems with them