High pressure is the critical aspect behind accumulators and storage tanks such as those found for tire inflation.
Your pressure requirements are quite low (15 kPa / 2 psi) which does not pose a danger for air storage. This means that common household items can be used.
You should be able to find a vehicle inner tube to match your volume requirements. If the tube is encased by a tire, safe pressure can be as high as fifteen times your maximum. Without the tire or other enclosure, the maximum safe pressure is likely to be "only" three to four times as high as your maximum.
Other reservoirs can be had in a safe manner. I've constructed air chambers using two liter soft drink bottles which hold thirty times your required pressure (un-modified) and when encased with fiberglass cloth and resin, more than fifty times the pressure.
You've noted that you have used tubing as a chamber, which could be expanded easily to a much larger diameter and length to match your requirements. Even ordinary garden hose is designed to handle pressures of fifteen times your maximum. Hydraulic hoses of various diameters are engineered to support hundreds of times your maximum pressure, but that's bordering on the absurd, based on your requirements.
It is not recommended to use PVC pipe as a pressure vessel, due to the explosion risk but for your low pressure requirements, it is a zero-risk situation.
Your options are nearly endless.