Bigger Freshwater Tank

Part of the reason for using so much water so quick, is the fact that there is myself, a wife, and 7 and 9 year old girls. My Fuzion came with that blizzard package, which means that i'll have to take the cover off the belly of the trailer to see what's all going on underneath. Looks to me that it has 3 43 gallon tanks for the gray, galley, and black tanks. The black tank is fine, but we always have to empty the gray which gets used the most from the bathroom sink and shower. The galley only gets used from washing dishes. I'm gonna have to do some calculating on upgrading the freshwater and the gray tank capacity. As far as toys, the only thing we really haul, is a Teryx 4. We've only done that once, and that was for a weekend trip. The trailer grossed a little over 19,000lbs, which is over the rating for the trailer, but not my truck. The thing about it,...for the short weekend trips like that, we don't have to carry all that extra stuff. When we went to Disneyworld from Chandler, we didn't take any toys, but we had to pack a lot of the extra stuff,...enough dog food for 3 dogs for a month, 4 five gallon water bottles, extra clothes, etc., the trailer was about 17,500lbs. In all honesty, i'd rather have the bigger tanks, and be able to boondock longer. I don't really worry about carrying around all that extra weight because my truck is very capable of handling it. I think if i have to, i might have to upgrade to higher rated axles, and then legally get it changed so that i can tow and not get hassled.