OK if you can handle the extra weight in the tow vehicle .
BUT!!! The holding tanks are usually sized to handle one tank of fresh water .
(100 gal fresh = 60 grey+ 40 black). If your adding more fresh you HAVE to drain your tanks , somehow ; and most RV's don't have the CCC to handle all three tanks full, when being towed.
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.