I used a monsoon for a couple of years on my Previous car (Stag) mine only lasted 2 winters, during the second one it began to deteriorate badly.
Worth saying that my car was a daily-driver, so I took it off/on everyday, so my usage pattern may not have been typical.
I ended up switching to a Hamilton classic moltex-type (bought via the club) which was excellent - a couple of seams began to go after 4 years, but my best surgical stitch-work with some leather-thread kept it going for another year when I bought another one.
I was impressed enough to choose the cockpit-cover from the same company for my current TR - slightly easier to handle and store in the boot - but obviously doesn't cover the entire car!
Hope this help..... Andy