Welcome Marlene...
LuvLabs has given good advice. I'd add a couple points. DEF fluid is DEF fluid. It all meets ISO 22241 standard. A Crows opine, is that you want to keep the cap and fill port surgically clean to avoid the "white creep". Same with the fill bottle...kitchen counter clean. If you use a funnel, get one only for DEF. Keep it clean and in a zip lock bag.
DEF evaporates leaving that creepy white crystal film on everything. That may not be healthy for your DEF system if if it gets inside the tank.
Opinions vary as to filling the tank. Some say use the "school solution" and wait for the Lo DEF light. Others favor refilling from time to time. This latter group seems to be growing. I'm in the latter group.
Just as crystals form on the outside of the neck and cap, I think it will do the same on inside parts of the tank when they are not wetted and "dry" out. So better to top it off from time to time to keep everything wet. Especially since it is an RV and not driven regularly.
