I dont know how big of a hog wagon you are lookin at building, but with mine hooked up to the wheeler almost fills up my 16ft trailer.. I bought my trailer just for hauling my wheeler and wagon without having to unhook every time to get it on or off..
If you have to haul it to where the wagon is on the trailer and wheeler in the truck, just leave the hogs in the wagon and use the boxes for the dogs on the ride home... JMO