80,000-20,000=60,000.
$60,000 buys a lot of fuel. You said you are "too old", so you may never exhaust this savings amount before you die. May you live a long life though.
The sprinter is stealthy and will fit in any high-dollar neighborhood without complaints, unlike that box van or a camper.
For $20,000 you can do a lot of cosmetic fixes on the outside of your old camper also, really less than $5k. New aluminum corrugated siding is not that expensive, even if a dealer replaces it.
If all you are worried about is fuel cost then you will never beat keeping old unit.
Consider insurance cost on a newer vehicle also.