Happy,
I installed a new gas cap on my viper about a month after I bought it. It's actually easy given the right tools.
You must be registered for see images attach
This is actually the gas cap kit I put on. It comes with a filler neck puller which as Drumr points out is something of a hooked hanger (although they provide a real genuine puller that makes like SOOO easy. It's a solid piece of pulled aluminum.
http://www.mgwltd.com/viper_gts_gascap.shtml
With that tool, getting the old one off and the new one on was maybe a 30 minute job and that's with all the wandering around and careful poking. The actual task of getting it back on was maybe 5 minutes. It would have been a tough job though without the tool. If a coat hanger works then have at it. Be sure not to puncture the hose though. Also a light bit of appropriate grease helps it slide on.