I would still go with the 1000.2. If you're going to aim a dish you might as well aim the 1000.2 and get all three satellites on the same dish. That way you won't have to switch the A/B switch when you want to change channels that are on the other lead. The other advantage is you can supply multiple TV's from the one dish with different programing. When you don't want to mess with the portable dish you can still use the dome and just 110/119.
I think you could use the 18" dish with 129 alone, but I don't think you will be happy with it. When you switch the A/B to the different dish you will have to run check switch to set up the receiver to the appropriate dish or set it up for both and have it constantly looking for signal when the signal is on the other lead.
If there's an input for a third orbital on your dome, then that would be the way to go, otherwise I'd go with a 1000.2.