Actually I don't have a coolant pressure gauge, not even at home. I did
check the hose clamps and they are tight. I took it to Culver's Auto Repair
in Missoula. He could see no sign of a leak anywhere so  told me to just
carry some 50% antifreeze with me.

We're at Flathead Lake tonight. I just looked under the van and there's a
small spot of coolant under the engine and some on the part of the head
under the small hose to the thermostat. Not as much as in Great Falls,
though. It felt dry under the hose. Weird.