AAA has a download entitled, Your Driving Costs. Fill out the calculator.
A "new" 4WD one ton Diesel is going to be 70-cpm (probably higher) at 15k miles per year given five years of ownership. Above $10,000-annually as a minimum. $12k is more realistic for the truck cited.
Fuel cost is roughly one half annual expense.
Where the cost of diesel is 20% greater than gasoline, there's no savings on fuel with choosing diesel. The diesel advantage is about work, and possibly about engine life once past 200k miles.
The real questions are about length of ownership. Both TV & TT.
My folks bought new. Had one TT and two TVs over 27-years (by choice) that were also my Dads DD. About 400k miles on those vehicles and full timed not quite ten years after early retirement. So, bought in their late 40's and sold in their mid-70s.
This justified buying far better than a white box of a TT. Their Silver Streak I think had an awning replaced and one AC unit. Might have been more, I just don't remember. Point was that with both, they were paid for long before a change was made or repairs needed. The quality was such that little was needed. Indefinite life span. That TT is now more than forty years old and still on the road.
I couldn't afford new, so bought a 3-yr old CTD, and a 22-year old Silver Streak barely used. Under $30k together. Get 15-mpg average towing this 35', 21-mpg overall annual average. Less than $500 in repairs in ten years. Trailer needs more, and if I spent $10k plus I'd still be ahead versus sale value.
Trying to say, look at both vehicles. Have a plan. Like setting a WD hitch, use real numbers. Be comprehensive. Longest life and highest reliability at lowest cost was what I wanted and got.
Helped that I'm third generation and understood this before vehicle spec (as a ten year old Airstream has flatlined in depreciation yet is better than any brand new square white box AND doesn't require a truck; further dropping costs several thousand per year), knowing ahead of time that saving on purchase plus TV fuel burn would save $3k annually over 20-years pays for the approach.
There's plenty to play with. The actual cost of your RV? Nights aboard versus years of ownership. Plug that in with a whiskey shot at hand. Five or six years is painful. Fifteen to twenty isn't.
By comprehensive, I mean look at also being able to park under cover. Garage preferably. Add that in. Construction. Sell the four bedroom house and get something that reflects prudence. If camping is important, make it so.
Since these discussions always tend to touch on fuel, learn -- be willing to change habits -- to alter DD so as to offset vacation travel expense. It's not hard.
CPM is a basic business tool. Use it.
The knuckle-dragger approach is thinking it's the monthly finance note and weekly fuel bill.
But no matter where one starts, cpm is a road to reduced cost.
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