I wouldn't be aposed to a diesel 10 years ago. Now I am all set with all the added emissions. I know the diesel gives a better towing experience but there is too much going on in those new diesels for my liking. Just the weight of the exhaust system on a new diesel robs over 100 pounds off the payload. Not to mention I have another 5 gallon tank of animal urine (DEF), heaters for the urine, etc. I'll stick to simple for the amount I tow.
I have a friend that does at least 5,000 miles a years towing a fifthwheel and he is a cheap sob. He didn't the math between gas vs. diesel and he found no financial advantage. He towing a fifthwheel similar in weight to the one I'm getting with a 2012 f350 srw 6.2 gas 4.30 axle.