Being able to drive doubles and HCT's out of their normally allowed areas is great so I firstly must say thank you for letting us travel most of the map with them! I just wish the no go zone would turn off during off peak times (when I generally get to play). It's a bit hard to find roads with other players outside of the no go zone when there's only 2000ish players on the whole map (Europe 2).
As for not having cargo on doubles, just redefine the doubles as singles. You can move them to any garage and take cargo with them like any other trailer then!