1. In 43 years as an RV tech, I have NEVER seen the 45 psi RV water pump go OVER 50 or 60 psi. NEVER
2. To have 2 pumps cause a 100 psi is out of the statistical possibility.
3. I have NVER paid attention to what a Water heater full HOT tank does to the psi. So, is the Water Heater ON when you travel? Possible missing or bad check valve on the water heater, or just the hot water increased pressure backfeeding thru the cold water input. Water Heaters usually do not have a check valve on the input but do on the output.
4. I would also suspect an inaccurate or bad Pressure gauge. Doug