Bought a few of those portable units that sit on the floor, when our whole house A/C bit the dust a few years ago. They worked reasonably well, though the output is not real high ... I think most of them are around 6000 BTUH. If your TT has just one roof A/C, you should notice an improvement with one portable unit. If you already have two roof A/C's, 6000 BTUH won't be much of a boost over the 27000-30000 you already have.
If you go that route, they require a vent hose to the outside of the TT. You'll have to rig up something at one of your windows. And the hose they give you with the unit is only about 6' long.