Google has been cracking down on this for years, and I would avoid setting up doorway pages for SEO. They came down on my company's web site a few years ago, namely the landing pages we were using for our paid search campaigns. We had a redirect in place, if the user didn't meet some initial criteria - and would send the lead over to one of our affiliates instead. Google viewed this as doorway pages too and warned we would be penalized if we didn't change this or make it more explicit what was happening along with an option for them to not be redirected.