Our trailer also has the old style plumbing - it is called polybutylene. I've replaced quite a bit of it with Pex over the years. The good thing about it is that you can use the Pex fittings on it that you can get at Lowes or HD. Just bring in a chunk of the pipe and you can match the fittings right up. Then you can add Pex tubing to wherever you want to go.
Also - yes you can use faucets from these stores to replace the standard RV ones - just check out how many holes there are in the mounting area. For instance we replaced our bathroom faucet with a bar sink faucet because there was no middle hole for the drain lever.