I actually had a 2007 Keystone Outback 210RS. Go with the 3/4-ton now and save yourself a lot of trouble. When I was loaded with passengers, dogs, fire wood, Kayaks + the travel trailer the rear end had way to much bounce in it. You will run out of payload on a 1/2-ton truck long before towing capacity.
The TV I used was a 2006 F150 5.4 3.73 Crew Cab max tow package. Upgraded to a 2008 F250 Extended Cab Diesel and the stability of the truck was a huge improvement, couldn't even feel the trailer push against the truck. With that said the 210RS is plenty light enough for any of the big three 3/4-ton gas truck to pull and be happy so doing it.
And something to think about that 2006 F150 got at best 16mpg on my daily commute which is 30 miles one way. My current 2008 2500HD with the 6.0 Gas 6-speed gets 14.5 on the same trip. If you do city driving your not going to notice a big difference either way.
My old man just purchased a 2012 F150 5.0 3.55 Crew cab thinking he would get 18mpg. He lives 5 miles from his job, all city driving and he has yet to break 12mpg. It's all relative really, the mpg numbers come into play if your doing straight highway driving and even then if you can't afford the gas bill for driving what I do then the next best thing would be to purchase a commuter car and an older crew cab tow vehicle.
2009 Ford F350 V10 4.10 FX4 Crew Cab SRW, Timbrens, Leer Topper