Before we got to Denver we called some RV parks that looked to be acceptable but all were full. I had looked for some BLM camping but found nothing less than 60 miles from the city. So, we've ended up at The Jefferson County Fairgrounds which is practically empty.
I was surprised to see that there were no propane restrictions like tunnels on the east coast. This is because tunnels on the east coast tend to go down under bodies of water, where heavier than air propane would collect at the bottom.