I was put in a position like that a long time ago (about 1980-1981).
My job would require extensive daily driving around Northern California especially around the San Francisco area. I didn't know how extensive it would be, but did know it would be a lot.
The deal: The company would pay me up to $100 per month towards a car payment or cash if I kept the car I already had, plus all the gasoline I had to purchase, PLUS all the gasoline i used for personal recreational purposes, and on the weekends (and the boss said, I swear, "But don't take your girlfriend to Maine and Bangor"
But, any repairs and insurance were to be my own responsibility.
I had a 1972 Buick Skylark Custom sport sedan at the time but it already had 140,000 miles on it and it was a real gas guzzler. The boss suggested I buy a brand new K car (Lee Iacocca's wonder) the Dodge Aries I think it was....yuccck.
I thought this was my chance to finally get my first Mercedes, so I went and looked at used 1977 240 and 300 diesels, and really liked them, but the bank wouldn't finance them.
So, I wound up with a very nice looking 1977 Olds Delta 88 Royale coupe with 39,000 miles on it, an ex- company car for a printing company in SF that I found at the Olds dealer in Oakland.
Oh man, I was driving all the time. It was over 1000 miles a week, every week, just for business. After that, I was too tired to drive places on the weekends. That's 48,000 miles a year!
I was taking the car in every other week for an oil change, and that car was luxurious, but it had it's share of problems, and it cost plenty to keep it going.
So, in the end it was a wash. I suspect the boss knew he was going to have me on the road all the time, and the deal didn't hurt him at all, and knew I would be too worn out to drive much for fun while he paid the cars's gas. The mileage I racked up was enormous. (So it was worth it to get a comfortable and safe car).
I'm really sorry I didn't get to buy the Mercedes 240 or 300 Diesel (there were quite a few nice ones around in those days). I might even still have it today. Not that Olds, after 100,000 miles it began to fall to pieces. It was junked LONG before 1990
Being on the road that much, get the car that suits you best. I'd think the van would be pretty uncomfortable, after a long distance drive, so after awhile you would really feel hammered, and let's face it, they are not the most comfortable, good handling or safest thing out there. But I wouldn't think you would want to use up your personal car in the service of a job either. Though your Benz is ideal for this kind of service, and comfortable, long lasting and safe, so it could work.
When you are out on the road every day all the time, you just about see it all, every possible scenario. May be best to face it in a safe reliable car like a Mercedes