Return it and get the correct (hole or plate mount) one
The reason why you don't hear foot mount transformers talked about is because they aren't intended to be used on their own -- they're intended to be mounted into equipment (say an air handler or an industrial control panel) where they can be nice and snugly wrapped up in a box that also contains all the wiring connections.
So, you have the wrong part for the job -- return it and get a hole or plate mounted transformer with the same electrical ratings instead. If you're stuck with a foot mount paperweight -- you could take a large NEMA 1 enclosure and mount it + the splices in that, taking advantage of NEC 725.136(D):
(D) Associated Systems Within Enclosures. Class 2 and
Class 3 circuit conductors in compartments, enclosures, device boxes, outlet boxes, or similar fittings shall be permitted to be installed with electric light, power, Class 1, non-power-limited fire alarm, and medium-power network-powered broadband communications circuits where they
are introduced solely to connect the equipment connected
to Class 2 and Class 3 circuits, and where (l) or (2) applies:
(1) The electric light, power, Class 1, non-power-limited fire
alarm, and medium-power network-powered broadband
communications circuit conductors are routed to maintain
a minimum of 6 mm (0.25 in.) separation from the conductors and cables of Class 2 and Class 3 circuits.
(2) The circuit conductors operate at 150 volts or less to
ground and also comply with one of the following:
a. The Class 2 and Class 3 circuits are installed using
Type CL3, CL3R, or CL3P or permitted substitute
cables, provided these Class 3 cable conductors extending beyond the jacket me separated by a minimum
of 6 mm (0.25 in.) or by a nonconductive sleeve or
nonconductive barrier from all other conductors.
b. The Class 2 and Class 3 circuit conductors are in-
stalled as a Class 1 circuit in accordance with 725.41.
...but it's probably simpler and cheaper to use the correct thing to begin with, even with the return involved.