Sod is heavy.
You will be at a distinct disadvantage with only a single axle tractor hauling a load of sod in a van.
A single axle tractor with a 28ft tandem flatbed trailer and a Moffet style forklift is a great way to do local/regional deliveries and can be profitable with the right contract in place. Most residential deliveries are less than 4 pallets and therefore you could put 2 or 3 deliveries on a short trailer at one time. A flip-over tarp like the rolloff trucks use can make covering quick and easy.
Single axle won’t be suitable. I hauled sod out of Minnesota to Ontario long ago and was always max gross with a 45’ flatbed and tandem tractor. Get caught in rain and the sod sucks up more weight as the screen tarp is a sieve