It depends on what you want. A light boat could be towed by something as light as a Ranger or F150 pretty easily.
It also depends on which type of diesel engine truck you're looking for.
The older 7.3L engines don't have as much power as the newer ones, but are widely regarded to have better fuel economy and less problems. The newer 6.0L and 6.4L engines get worse fuel economy and have been known to have their issues, but are very powerful.
Any diesel truck is going to cost much more to maintain, it's just the nature of the beast.
I'd recommend an F150 for your use. The better retained resale value of a diesel is offset by the increased maintenance cost, and gas SDs really drink a lot of fuel no matter which one you get. An F150 would get reasonable MPGs and provide plenty of towing power for your boat.
I agree with Tom. A F150 crew cab would fit the bill just right. Not sure what the newer 6.2 is getting for fuel ecomony but I know the 5.4 would do pretty well on the open road and you can put well over a 100K on that motor.
I would have to agree with the other two as well. The biggest thing that would have swayed me would have been the weight of the boat, but relatively speaking isn't that heavy.
Plus, I noticed that you said new truck, I don't know if that means new to you or flat out new truck, but the new 2010 F-150s have a 6 speed tranny with a T/H feature(like the F-250s and up have) that is a really nice feature. I like it on my 6.0, not quite as "in your face" in my 150, but it's still pretty good and I think would handle that boat fine.
Ultimately it depends on what you want and what you feel that you can afford, but I think a new F-150 would be a nice towing, and DD commuter for you much more so then the heavier vehicles.
I agree with the tex, Scott, and Tom. For that use a F150 might be the better option. I know the 2010 F150's are getting much better mileage then my F250 and they will still handle a 2500lb boat without breaking a sweat.
I'll throw my vote in for an F-150 as well. I've had all three (F-150, F-250 with V12 Gas, and F-150 Diesel). My experience is that it really came down to the towing configuration. By themselves, not towing, you'll come out ahead with the F-150. Add a light trailer load, and by that I mean a relatively light boat like yours, and you're still probably ahead, or at least even, with the F-250s.
It's when the heavy towing loads get used that the diesels shine. Pulling a 30', 7,000 - 8,000 lb travel trailer, I was getting about 6-7mpg with the F-150 (ouch!) and about 10-12mpg with the F250 V12 gas (still not great). But the MPGs were pretty much in the norm on the F250 diesel (6.0L), with or without the trailer.
If I was driving 40k miles a year and didn't need the truck for the commute I would have two vehicles. A truck for any towing hauling needs and a more fuel efficient vehicle for the commuting. An F-150 would handle that size boat fine even though a 22' center console fiberglass boat, with trailer, motor and etc will weigh well over 2500lbs, probably closer to 5k lbs. A 5k lb setup isn't an issue for a properly equipped F-150.
Definitely considering getting a separate commuter car. Putting that many miles a year on a new truck will just kill the value fast. Also, if you go diesel, regular oil and fuel filter changes will add up $$$ fast. I'd get a gasser truck to pull the boat since it isn't very heavy, and a little Civic or Focus to drive to work.
It's really going to depend on how he gets that second car to. There are still going to be additional monies going out for a second car that's going to cut into what savings he could get by having a car for commuting and a truck to haul.
If he is going to keep it 4+ years, I would be less worried about the miles(and value) then I would be if he was going to trade it in in 2 yrs.
If he gets a separate car which gets 40mpg instead of a truck which might get 20mpg, he'll be saving $3000/year in fuel. That would pay for a brand new focus in just a few years.
That's if he realizes that mpg. I've always been far less then what the average claim in on mpg for whatever vehicle I have. No matter how I drive it and I'm far more conservative then you would think considering how one of my vehicles is modded.
Even the few times that I drove the ole ball and chains cavalier on a few road trips I got 18.7 mpg. I don't know how he drives and where he drives, those are going to be important factors that could help hinder him or not.
It could really be that no matter what he gets, he'll see crappy mileage.
This, of course, isn't going into rather or not he is going to have payments on a new one. If he buys used, how used is it? Is it a money pit? etc.