Implementing ISerializable for Properties.Settings (.NET 2.0)

I have a Dictionary<MyType> that I want to store in my User settings in user.config.  I know that Dictionary<MyType> is not serializable so I've tried to implement ISerializable on Dictionary<MyType> to serialize Dictionary<MyType> as a List<MyType> but this doesn't seem to work (even though I can get List<MyType> to serialize to app.config directly). 

What am I missing?

Here's my code:

using System;
using System.Collections.Generic;
using System.Text;
using System.Runtime.Serialization;

namespace MyStuff
{

    // Settings of type Deployment serialize to user.config with no problem
    [Serializable]
    public class Deployment
    {
        private string _Key;
        private string _ShortName;
        private string _Name;
        private string _URL;

        public Deployment()
        { }

        public Deployment(string key, string shortName, string name, string uRL)
        {
            _Key = key;
            _ShortName = shortName;
            _Name = name;
            _URL = uRL;
        }

        public string Key { get; set; }
        public string ShortName { get; set; }
        public string Name { get; set; }
        public string URL { get; set; }
    }

    // Settings of type DeploymentList serialize to user.config with no problem    
    [Serializable()]
    public class DeploymentList : List<Deployment>
    {
        public DeploymentList()
        {
        }

        public DeploymentList(Deployment deployment)
        {
            this.Add(deployment);
        }
    }

    //  - Breakpoints in GetObjectData and the constructor never seem to get hit
    //  - Although I see the root of Deployments in user.config when I save it,
    //      the DeploymentList property contained by Deployments doesn't get serialized
    public class Deployments: Dictionary<string, Deployment>, ISerializable
    {
        public Deployments()
        {
        }

        public DeploymentList dl;

        public Deployments(SerializationInfo info, StreamingContext context)
        {
            dl = (DeploymentList)info.GetValue("DeploymentList", typeof(DeploymentList));
            foreach (Deployment d in dl)
            {
                this.Add(d.Key, d);
            }
        }

        void ISerializable.GetObjectData(SerializationInfo info, StreamingContext context)
        {
            dl = new DeploymentList();
            foreach (Deployment d in this.Values)
            {
                dl.Add(d);
            }
            info.AddValue("DeploymentList", dl, typeof(DeploymentList));
        }
    }
}

<?xml version="1.0" encoding="utf-8"?><configuration><userSettings><MyStuff.Properties.Settings><setting name="DeploymentList" serializeAs="Xml"><value><ArrayOfDeployment xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                        xmlns:xsd="http://www.w3.org/2001/XMLSchema"><Deployment><Key>Test</Key><ShortName>Test</ShortName><Name>Test</Name><URL>http://test.com</URL></Deployment>                    </ArrayOfDeployment></value></setting><setting name="Deployments" serializeAs="Xml"><value /></setting></MyStuff.Properties.Settings></userSettings></configuration>