Renting Westfalia van to tour Germany and Poland

My husband and I are interested in trying to rent a Volkswagen Westfalia camper van in Amsterdam or another location and driving around Poland, Germany, and possibly Slovakia and the Czech Republic in September. I would appreciate hearing from anyone who had done this style of camping in Europe. Please share your experiences, along with pitfalls, and benefits. It seems to be a cheaper way to travel. Are camping areas difficult to find? We have food allergies, so do most of our cooking rather than eating restaurant meals. Does anyone know of companies besides the Amsterdam one that rents these camper vans?