You could probably get pages and pages of debate going on gas vs. diesel reference the costs of ownership.
If you end up with a Class A diesel it would be kind of hard to predict your exact maintenance costs.
Your engine will require $140 - $200 oil changes, fuel filter changes, on a regular basis. As your miles build there will be other maintenance that has to be done not to mention tire replacement, shock replacement, etc.
We budget/spend around $150 a month, or about $1,800 a year in maintenance costs for our TV, but we currently put a lot of tow miles on it.