I would think you could find a small toy hauler that you could pull behind a 1/2 ton truck but not sure ...
if you got an equalizer type hitch with sway protection, that might help with off loading tongue weight but if you get a regular travel trailer (non hauler type), remember with 3 bikes (full size) you will already have about 750 lbs in the bed before hooking on to a trailer and most travel trailers have a pretty heavy tongue weight (equalizer hitch would help). you need to check the GVW on the truck and towing capacity before deciding on what you buy trailerwise. I wouldn't think a 3/4 ton wouldn't be all that much more expensive over a 1/2 ton (relatively speaking) and you get much more heavy duty towing capacity.
either way you go, your fuel consumption while pulling a trailer will be pretty poor unless you opt for a diesel (then you pay more for the vehicle up front and more per gallon for the fuel but should last you much longer with fewer repairs).
while my son was riding the enduro circuit, we opt'd for the bikes in the truck and a tent for the majority of the races since they ranged from 150 to 600 miles from home (80+mph with a RV in tow for 5-8 hours not a good idea). now that he isn't racing for points, and we make family outings, we got a bumper pull 28' travel trailer with slide that says it will sleep 6 (but they better be really friendly
in the table and couch converted to beds, so 4 adults comfortably) and can get 3 full size bikes in the truck bed (dodge diesel quadcab longbed 3/4 ton), take the whole family and still average about 14 mpg unless bucking a head wind. we haven't tried 3 bikes and generator yet, but 2 work fine. likewise, for shorter trips, I don't even worry about the equalizer/sway hitch on my 3/4 ton but do use for longer trips. now the wife doesn't mind going with us since she has a traveling conveniences of home (almost).
the toy haulers are a great idea but there are some draw backs as stated earlier, but some do have onboard fuel stations built in, so no gas cans for the bikes needed (so just fumes off the bikes). also onboard generator would be nice too.
likewise, be very leary of tandem towing two trailers and I would only do if the front trailer was a gooseneck/5th wheel. I recall someone posted a year or so back about tandem towing two bumper pull trailers was illegal in TX but I can't find the law on that anywhere.
let us know which route you decide on going...