Hi Dan
It would depend on what time you are arriving at Fishguard and how much driving/traveling you have already done, I have just checked with AA autoroute with the speed set for towing and it indicates that it will take approx 6 hours add breaks ( 3No-max driving time 2hours) to this and possible traffic delays , it could be a very long drive. I would, probably based upon this info I would stop en route.
Hope this helps
Alb