The back of the van is 5 1/2 ft wide, 4 ft high and 9 ft long. The 9 ft is measured between the back door and the back seat. If you take out the back seat that will add another 30" of floor space.
Each bag of mulch is approximately 31" long, 21" wide and 6" thick. Volume wise - 88 bags. (This is in reference to FeF on-site stuff, right?)