Battery Disconnect

I am new to forums so apologize if this has already been addressed! Hoping someone will help!

I am wanting to tow my 08 Smart ForTwo behind my class C RV. The Smart has been equipped with the base plate, tow bar... by my local rv dealer. They told me that I need a battery disconnect and to contact the dealer. I spoke with my local dealer and he said that they can not order one. Which I'm having a hard time understanding this since the manual states to contact a dealer. They say that it is an after market part. I am having problems finding the part or knowing if I have the correct part when searching for it. Can you please share the part you have used and part name and number? Thanks! Also I spoke with someone who has towed a Smart and they said they had to bungee the steering wheel due to the wheels not straightening out after a turn. Wondering if others have this same issue.

Thanks for your help!