Bill,
The plastic container is the expansion tank for the antifreeze solution. If Lazy Days drained and replaced the solution, they would have probably removed the large "radiator cap" on the top of the unit for re-fill. I think this would have been shown on the bill as a complete refill takes a significant amount of anti-freeze. In this case, it follows that the tech failed to refill the expansion tank to the Cold level. You can open the Radiator Cap to see if they refilled the unit (Make sure unit is cold) or add solution to the expansion tank as it drain into the unit. Since you said it's been a few weeks since the work was done and assuming you've used the heaters in the coach, my guess is that they failed to refill/recap the expansion tank as a system shouldn't have heat if there was no/little anti-freeze. Solution in the expansion tank should be at the Cold level. I found that after draining, I had to add solution to the expansion tank a number of times until the unit was finally "full".
Steve