Bongo Fury

Recently I towed my very small, light boat home and had to bring it up a long but not particularly steep hill, when the temperature rose enough to set the Mason alarm off. The alarm is set to go off when the needle reaches the white line on the gauge before the red. Since then, my partner (who drives it daily) thinks the gauge is reading higher than it used to. I haven't had a chance to look at the gauge while she's driving to see where it goes to, but the alarm hasn't gone off since...should I be worried?

I checked the water level before leaving on the trip and it was exactly on the max line

we had this problem towing our caravan, till i put on a new radiator and realised that there was no real chance of coolant getting round as it was pretty blocked up. check for cold spots on the radiator and if the bottom hose is warm/hot. maybe like ours was and it isnt getting good flow round the radiator, stat could be an area to look at also. ours now runs below midday with the mason on, only had the alarm go off once since, that was pulling 22' caravan up a steep hill and alarms set just over 4