If I were going to buy a new one, I would buy one from JD Skiles in Atwood, KS. If I were going to buy a used one, I would study the design of the JD Skiles trailer and rig it up the same way they have it. Their setup has everything you're asking for, plus one very important addition:

They have a number of (more or less depending on how you specify it) stainless steel tanks on the side of the area where the shuttles sit. These stainless steel tanks are shaped like a very tall cylinder. You can probably specify how much you want them to hold, but they are most likely 40 or 50 gallons a tank. You pull a vacuum on these tanks with your sprayer. Then with the valving they have set up, you can suck product out of your shuttles into the stainless steel tanks. They have sight gauges and capacities listed so you know how much you're sucking out. After you have measured out the correct amount, you re-route the suction with your valves and you can then suck out of the stainless steel tank into your sprayer.

The advantage of this is that you do not have to have any pumps or meters on your shuttles. In our experience, both the pumps and the meters are a major wear item and I can't even imagine what you'd have to do to wear the stainless steel tanks out so eventually it will pay for itself that way. The other advantage is that it is MUCH faster than using the traditional pumps that you would have on the top of your shuttle. Especially with thick chemicals like parallel plus. If you are pressed for time, it will pay for itself that way as well.

To my knowledge my neighbor is the first person who came up with this design. He is a large farmer in the area. He's been using this for probably 5+ years now. Someone asked JD Skiles to make another one like it for them, and they are finally starting to bring it into production. If my neighbor was not the first one in the country to do it like this, I still applaud his creativity because he is unaware of anyone who has done it like that before him.

Anyways, you can go to the JD Skiles website for their phone number (it looks like their website isn't in very good shape) and talk to them about their semi nurse trailer with stainless steel product suction tanks to learn more about it. Just say you would like to talk to someone who knows about them. I can tell you for sure though, that kind of a trailer is really the way to go to keep a one man band going if you're at all spread out. You can reload your sprayer in probably 10 minutes from the time you hop out of the cab to the time you hop back in with this setup. We would have this setup but we've got a considerable amount of investment in pumps and meters now. As our pumps and meters fail, we will probably convert over to this system one tank at a time. I would highly recommend you take a look at this setup, just for design ideas if for nothing more. It is quite creative.