When comparing costs, you must compare the opportunity cost of buying the truck and camper vs investing the money. Since if you didn't buy them, you could in turn throw that in the market and make $$.
I don't think there is a ton of financial justification for weekenders and part time RV'rs. You buy these things because you love the lifestyle and the costs are what they are.
Now the longer you use the unit, the more the numbers can get skewed for financial gain. There are scenarios where living full time or most of the time (especially expensive areas) in an RV can save you $$ and be great investments into the future. Assuming you stick with the plan and don't get the upgrade bug every 5 years or so :)
It can make sense financially in some cases, regardless the extra cost may be perfectly reasonable to have your own little house on wheels to enjoy the great outdoors. Even if it costs you more.