The expansion tank/accumulator will act same as the air pocket and absorb the increased volume/pressure and avoiding the spike that would otherwise be created by the expanding water. Can be installed anywhere between the pump and water heater. Basically it is a permanent air pocket.
I had an issue a decade ago where the spike in pressure was causing a leak at the pump. Very hard to detect due to the intermittent nature. Dealer failed twice to find the leak.
And yes I did notice a spike in pressure when the hot water was used up and then no water was used while it re-heated and expanded. This is when I realized the issue and found the leak.
I had an apartment building doing the same thing except it has 2x 100 gallon water heaters. I was having leaks soon after the water company required a backflow device on the main water supply. My plumber put a 2 gallon expansion tank on each water heater and the issue stopped. Leak under the slab was costing $4,000+ each time.
I recommend an expansion tank for all closed water systems including your home or the RV. It really works.
