I worked on E350 and E450's from that era with the V10. And later I drove one on a daily route (drivers were paid more than mechs and I had both skill sets....hmmmm).
As a bus on a lightly loaded (75% of capacity was rare) they did fine but I lived in the flatlands where they grow tens of thousands of acres of rice (a flooded field has to be pretty flat) and tomatoes (open irrigation also requires flat land. We may have had a 300 foot elevation difference on the routes and that's a high guess).
I don't like the V10 as much as the 7.3 diesel from 2002 (and prior) but it seemed okay.
HOWEVER, with a E### you have a large chunk of the engine in the cabin which means a lot of it is going through the firewall and access is VERY limited there. I don't remember if it was the E350 or 450's but we actually drilled holes in the fender wells in order to get to a couple of the spark plugs in order to get to them without cutting ourselves up squeezing through. Just food for thought.
As for the chassis, look underneath and check the condition of the exposed floor. Many were made with just plywood decking over a framework. Some were undercoated, some were just BARE WOOD. I wouldn't touch one with bare wood!!!!!!!!
Another major concern is that most of them around that time had massive computerized control boards in the space above the drivers head inside the front bulkhead. Those boards were a nightmare when they broke and because they controlled all the safety interlocks, a bad component meant an immobile rig. The interlocks can be removed but it takes a bit of electrical knowledge and skills (schematics don't hurt either).
Other than that our biggest problems were brakes (they simply weren't up to the stop and go usage) though as an RV that shouldn't be an issue....AND..... operator error (one drove into an overhang and took out the front 5 plus feet of the front cap).
They also generally have fairly small fuel tanks as the bulk of the market uses them as short distance rigs. They're not smaller than a standard E450 but they're not long distance tanks either.
So the biggest takeaways:
Check for a non undercoated wood floor on the underside
Check for any sign of trouble in those control board(s)
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We've done so much, for so long, with so little, we now do the impossible, overnight, with nothing. US Marines -- 6531, 3521. . . .Ret ASE brakes & elect. Ret (auto and aviation mech). Extra Class HAM, NAUI/PADI OpenWater diver