working backwards--starting out with this truck

One ton Dually, even an older one should be able to handle a fiver up to around 35 feet easily. You wont win any races when towing, but it should be no problem. Just dont expect to handle the likes of a Teton or Mobile Suites and you should be fine. Start looking at maybe a Cedar Creek, Montana or even an Arctic Fox with a place for a washer. You will probably find that in the 30 foot range they will be practically non existant. But moving up to 35 feet you should find lots of good choices.