If you want to implement your own solution by using GPdotNET library you have to got deeper knowledge of the project.
Projects GPdotNEt.Core, GPdotNET.Engine are the same for all GP models. The project and GPdotNET.Tool.Common contains separate implementation for each GP/GA problem.
To start with new Custom Model in GPdotNET you have to do the following:
 Modify void LoadModelWizard(GPModelType model ) from Main Windows.cs
 Implement Custom TabPage for you problem.
 Define you representation Chromosome or use existing one.
 Modify GPFactory class if needed.
__It is not so easy to use this library to implement your own problem solver, because you have to implement Simulation of the problem not only calculation.
Regarding TSP problem please look the following methods:
 MainWindows.LoadModelWizard(GPModelType model )
 TSPRunPanel.cs from GpdotNET.Tool.Common
and related classes and types.
