Unless you have a specific reason why you need to use a Liberty Gunboat instead of other Gunboats freely available, then why not consider an alternative that comes with less hassle?
And the idea of not allowing him to have the forward gun on his Liberty Gunboat (whoever said that) is rather stupid. There are no civilian forward cannons, and mounting a regular gun would throw off his aim. Further more the forward cannon is only class 7, I think, which means his choice of guns is... well, weak. He could mount a missile on there but... Neutralisers and Lancers... the point is other than the forward cannon there is not much of any other option for a GB.