Due to many legal issues too numerous to discuss here, you are playing with fire without a contract.
This industry is chock-full of people like yourself that trusted the vehicle owner by a handshake.
Spend sometime reading through the newbie section and you will see what I'm talking about...
First things first.... Get a contract spelling out what you are responsible for and what the van owner is responsible for.
After you have said contract then you can worry about all the rest.
You are an independent contractor, contracted to operate the vehicle for him. You do have a contract, dont you?
He could be, but not necessary. Does he find the load? Is he leased to another company?
Several factors are involved.
You would be a contract employee. It gives you the opportunity to learn the business. You don't know how much you don't know. Learn it on someone else dime. Use their equipment to learn.
Before spending any good money, may I suggest driving for a fleet owner for at least a year to learn the business. There's more to it than turn key & drive.
Remember, everything you add to your gutted van weighs something. This weight must be accounted for.
I'm not and never was a van driver, but it sounds like you're trying to reinvent the wheel.