CV Boots soft and supple?

Is there something to apply to the rubber boots to make them last longer? silicone maybe?

Won't hurt (other than trapping surface dirt) but it probably won't help either. IMHO

DK, you're close to Watauga aren't you?

Nothing - IMO.

Anything you put on would probably attract more dirt, which would lead to greater friction. Beyond friciton I would think that the greatest affect would UV, but being under the car this shouldn't be to significant.

I just try to keep them clean and free of grit.

HTH

A while back some company was offering an assortment of replacement boots made of silicone. They were blue and very supple. I measured the big and small diameters as well as the overall length of the boots on my old ZJ and used those dimensions to order some replacements.
They were touted as being impervious to cold weather.

Truth is all CV boots stand up just fine to the cold. I haven't seen them offered for awhile, but I haven't been looking.

Last time I replaced a CV on the wife's Subaru, I sprayed some Boeshield T-9 on a few of the rubber parts and was amazed at how it absorbed in and made them look more supple, almost instantly. I sprayed all the rubber bits under the car and they all seemed to regain some life.

I had it around because I use it on my mountain bike, but it was actually developed for aviation (at least that's what they claim).

http://www.boeshield.com/t9info.htm
http://www.boeshield.com/index.htm