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If you put the Fat load-dump TVS downstream of the reverse-polarity protection MOSFET [^1], then the load dump current would have to flow through the MOSFET.  The MOSFET would have to be rated for that current.

If you put the Fat load-dump TVS upstream of the reverse-polarity protection MOSFET, the load dump current would not have to flow through the MOSFET.  But the MOSFET wouldn't protect the TVS from the reverse polarity.  You'll need a fuse further upstream, and it would open when the TVS starts to conduct due to reverse polarity.

[^1]: Reverse polarity protection element in general.  In this case it's a MOSFET.  But it could be a Schottky in some cases.