I'm based at KGPM, great airport. You can park at the main FBO, and the self serve pumps are right there as well. Access to the ramp easy, either just walking through the terminal and out, or by one of the gates. Even if it was locked up tight, there is enough traffic from other pilots that could get you through one of the access gates, but really accessibility shouldn't be an issue. I'll PM you my info if there are any questions I can help with.
Lynn