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.

I don't know what you spray or how you do it, but I will explain how we do it. We have an old (1998) Patriot 150 sprayer. If you're not familiar, it's a pretty small, old self propelled sprayer made by Tyler (before Case bought the Patriot line). 150 HP, 75' booms and 750 gallon spray tank. Our spray tender is a semi pulling an old combine trailer. On the front of the combine trailer we have a 3200 gallon tank for water or fertilizer depending on what we're doing. Behind the fertilizer tank there is room for two shuttles and another 100 gallon tank for 24D. There is also an area for whatever things we may have in 2.5 gallon jugs.

In the last five years we have probably never covered less than 20,000 acres in a year with this rig. Some years it has been significantly more. It is almost always a one man operation. The only time we need someone to run the semi back and forth for product is when we're streaming 32-0-0 on and we're putting on 30+ GPA. Most of the time our product rates are much lower than that and only one person runs the sprayer and spray tender.

The first key to covering a lot of acres is to avoid having to deal with water treatment during busy times. We have a 1500 gallon tank at home that we use as a water reservoir for the spray trailer. We run a garden hose with a float on it into the 1500 gallon stationary tank. When the semi pulls in to the yard at night we stop at the tank and start pumping that 1500 gallon tank into the 3200 gallon tank on the semi. As it's pumping we pull the forklift up to the 1500 gallon tank with a pallet of AMS on it. We dump 5 bags of AMS into the top of the 1500 gallon tank and then let the water start going into the top of the tank again with the garden hose. By the time you've emptied your 1500 gallon tank you've probably put another 25 to 50 gallons of water in it. The next morning, you get up before you can start spraying and you repeat the process. You now have over 3000 gallons of treated water in your semi.

We are also very careful to make sure shuttles are full before we need to start a spraying day. We also make sure maintenance is done in the off time. Even if it's not due yet, but it will fall during a busy day, it gets done ahead of schedule. Finally, you have to be making your first pass as the sun is coming up or earlier (weather allowing).

If you follow these steps, you should be able to pull off 800 acres a day with your 4830 without sweating too much. The only problem is that you probably won't be under 80,000 pounds because a 4830 is significantly heavier than our Patriot 150. If that's not important to you then you're still good. If it is important to you then you probably need to leave with a little less than full capacity on your water. You can have someone bring a nurse trailer behind the pickup full of water to fill the semi just once a day and you'll still be able to get 800 acres a day. If you push hard and the weather cooperates, you'll be able to do more than that (depending on your boom width and field sizes/shapes and the distance between them).

I put together something similar to what you are doing a year ago.  We found a 9 year old 48 foot drop deck trailer for $13,000.  We put a 4250 gallon tank on it for $4,000.  It has baffels in it.  We put the tank on the lower portion of the trailer, which I felt made it feel and look safer.   We had a guy put a dump valve on the rear axle of the spread axle so now it turns corners sharp.

When I was looking I talked to the folks at www.jetcompany.com and they would build me a new trailer any configuration I wanted, and the price they quoted me was in the low $30,000 range.