Examples on Extending MembershipUser Object

[mark d.]

I've been working through the new features in 2.0 for about a month
now, am at the point of trying to apply them to my e-comerce
applications. My apps assign a unique custid field in tracking the
user throughout their visit. (ie, XYZ20001)

I've found a couple of examples on how to customize the
membershipprovider object:
<a href="http://www.devx.com/asp/Article/29256/1954?pf=true">Writing A
Custom Membership Provider for your ASP.NET 2.0 Web Site</a>

I've created a catalogmembershipuser object that inherits from the
membershipuser object. I add a property called custid. When I try to
change the return type from membershipuser to catalogmembership user in
my provider I get an error, can't override. When I remove the
overrides I get the shadowing warning.

I would love more examples on how to accomplish this or any insight on
alternatives.