As someone who had done much in trucks of all sizes and who has been a salesman, I fall back on the "good" salesman aspect and ask probing questions.  A good salesman will ask questions to determine what the CUSTOMER wants instead of trying to sell what the SALESMAN wants to sell, generally because of commissions.

First of all, will you be part-timing or full-timing?  Keep in mind full timers either have practically everything they own in the fiver or they store stuff with family members or rent space.  A part timer has a home within which to keep most possessions.  This is a factor in how much the camper will hold.

Second, what is it about diesel that drives you nuts?  If it is the noise, then go and listen to diesel trucks.  For instance, the newer Fords are very quiet running.  If it is the smell, there isn't much else to do but go with a gasoline rig.

Third, are you sure about a 7,000 pound fiver being able to hold 3,000 pounds of stuff?  That seems like a high number for such a small trailer.  I know of some larger units that don't carry much more than 3000 pounds, depending on what options were added to the camper.

Fourth, are you dead set against dual rear wheels?  While single wheels may well help fuel mileage, dual wheels greatly increase stability when towing a fifth wheel.  They also help with handling the "pin weight".

Fifth, and perhaps most important, how many people (and possibly pets) will be using this camper?  Obviously, the larger the number, the bigger the camper needs to be.  That effects the "stuff" part of things.

While you may not like the long box of a one ton, they can be helpful in carrying things that will be needed, but would overweigh the trailer if those things were put in it.

I think you may find that a gasoline engine equipped vehicle will be able to handle less weight than a diesel.  4 x 4 can be helpful, but it can cost you a little weight capability.  For instance, the Ford F450 2wd with a diesel, equipped right, will pull 24,600 pounds.  The same diesel 4x4, equipped the same, will pull 24,200 pounds.  Granted, very little difference, but still a factor.

Keep in mind that GVWR applies to each individual unit (pickup or camper) and what that unit will weigh with everything included, i.e. water, fuel, groceries, etc.  Neither unit needs to be overloaded.  So, a truck needs to be capable to handle the weight of occupants, fuel and any payload in the back, including the weight applied by the "pin weight".  THEN, the weight of the two units combined (GCVW) must not exceed the capability of the towing vehicle.  Thus, both GVWR and GCVWR must be considered.

Fortunately, from what you have written, you have time to research this thoroughly.  Leave no stone unturned.  Even turn over stones in forums to get the answers you need.  Many will tell you to pick the fifth wheel first to account for the size you need and THEN look at a towing vehicle.

If you exceed the size of vehicle you WANT to drive with the choice of fifth wheel that you WANT or NEED (due to space needed), then you may have to rethink everything.

Whatever you do, don't get discouraged.  I've been researching, test driving, peering at weight specs in truck door frames and asking questions everywhere.  I think I am getting there.

Also, you will get lots of GOOD advice from those that frequent Howard and Linda's site.

Enjoy.

Terry