Could the OP post which Torklift box and RV that they have? A description of the tongue area or a picture would help too.
There are a few threads on the Forum about installing the battery boxes. Basically, you will need to drill some holes in the bottom of the box and through the trailer tongue frame. Torklift includes self-cutting fasteners with the box. You can use those or choose your own fasteners.
I have a Power Armor DH A7700 (26 1/2" L) and it has two slots in the bottom 8 1/2" apart. The slots are 4 1/4" from on center. You may be able to use the factory cut slots and attach to an existing battery tray, should you decide that is the best manner of mounting.
The Power Armor box comes with instructions.