Paul,
Sounds like you have probably the only software I know of that works under Linux. The next big hurdle is getting a decent USB to serial converter. Given raster charts you can get by with a less powerful computer. Vector charts require a lot more horsepower.
This is one of the good USB serial adapters that I know of and they seem to have Linux drivers too. That rules out about 90% of the rest of them.
USB to Serial USB adapter Cable converter adaptor
You can find a lot of USB serial adapters on the Internet that are a lot cheaper and don't work. So save money and get a cheaper one and throw it away. This one isn't that much money and it really does work well for a GPS. They have distributors all over the world too. If you need special cables they also have links to get those as well. I have had mine a few years now and it always works great. I run Windows not Linux but since they have Linux driver support I can't think of anything better.