Full tank here as well when we travel but we do a lot of camping without hookups so that is part of the reason. Secondly, we have found poor water quality at many campgrounds that we prefer not to ingest. Depending on the size of your FW tank it amounts to carrying an extra person or two, I guess some are very close to over-loaded if a few hundred pounds makes a difference in towing. We see no discernible difference in mpg when towing with or without full FW tanks and our towing combo is well matched so zero issues with towing performance. Heck, there are many times we don't even pull out the water hose when only camping for a few days.
