No battery expert here but I do know that there are other brands out there that get mentioned here. Titans are supposed to be very good.
I would stay away from the dealer. Charging $100 to install two batteries is a bit steep in my opinion. You simply set the batteries into boxes that will accommodate the size. They have to be wired in series which simply means you will need to connect them with a sufficiently sized cable. Connect the negative of one to the positive of the other and you will be set. Connect the negative ground from the trailer to the negative of the first battery and the positive cable from the trailer to the positive of the other battery. That is it. To charge $100 for this is taking advantage of the customer.
I bet if you look at the brand name of the batteries they are selling you will find them elsewhere for far less. JMHO