If you make up a longer hose, is it going to fit back inside okay wherever it goes in your TT? Maybe a removable extension hose would be better for this reason?
How long do you need? Phoenix makes one that is 72" long, which from what I can find is the longest one available for an RV.
72" RV shower hoseThe other thing you could try is to take the hose into a plumbing wholesaler and see what they can offer. Sometimes wholesalers have parts and pieces that retailers don't carry. I use one here all the time that also has a retail/wholesale bath and kitchen shop attached that has a whole lot of faucets and accessories and other stuff I can't find anywhere else.