Elsewhere, you asked for some input so here it comes, for better or worse:
First, I would point out the obvious. That this is electricity we're talking about. Approach with caution. Even 12 volts DC can hurt. Ask anyone who perhaps has shorted out a ring on a finger to ground through a wrench while on the positive terminal of a battery. You might weigh the consideration of having it professionally installed by an RV service center. Assess your technical know how and judge whether this is something you should take on. Perhaps a division of labor is in order. Perhaps have the AC brought into the trailer and the converter hooked up by an RV place. Then, you wire the AC receptacles and the DC applications??
Otherwise, I'm probably going to tell you what the others have said, probably in another way.
Combination Converter/Charger/Breaker/Distribution
You asked for a common package. Parallax (used to be Magnatek) is in scads of RV's, probably just because they offer just such a combination package. I had an earlier 6300 series converter but upgraded to the 7300 series. To be precise, the 7345RU unit is just the converter that you wire into the space the old 6300 series converter was. It reuses the circuit breakers and fuse panel. The circuit breakers are for the 120vAC and the fuses are for the 12vDC.
The newer 7300 series has filtered DC current to all the fuses which in my case eliminated electric noise in the radio and TV. It also has a smarter charger that is less likely to cook the battery.
Are there smarter converters out there? Yes, but none that I know of with the combined converter/charger/distribution package. Ed references marine chargers and they do tend to be better in that they recharge faster. (I like Xantrex) However, there is an attraction (for me) to having it in all one package like the Parallax.
In this case we're talking about the Parallax 7345, about $270 without the AC circuit breakers. Circuit breakers are about $5-$7 each at the home store.
Ed's 7400 model simply has the "guts" of the 7300 without the distribution panels. I say panel
s since there would have to be an AC panel for shore power. The 7400 would plug into a receptacle fed from the AC panel or be hard wired into one of the panel's circuit breakers. Then, the output of the 7400 would go into a DC panel for distribution. Here's the system diagram from Parallax.
Click to view attachmentSpeaking of the 7300 series: In broad terms, the AC enters the converter/charger and into the circuit breakers. Some is split off through the circuit breakers to pass on the 120v outlets. Usually, one circuit breaker sends AC to the charger/converter side. That's because, even though it's one box, half of it is AC (and it's distribution) and half is DC (and it's distribution). The converter/charger get's its AC input from a circuit breaker. It's sort of the door between the two halves. This is so you can disconnect/protect the converter/charger side of the box.
I would suggest placing the converter/charger as close a possible to the battery. Parallax recommends 8 ga. wire if the battery and distribution panel is next to the converter. I'm conservative by nature and would upsize the wire (a smaller number) if the battery were more than a foot or two from the converter/charger.
Given a 7 pin connector, one of the wires is often labeled battery charge. It goes (eventually) to the plus side of the battery. There will also be a negative or ground. (Geekiness follows:) DC battery sources (battery, charger or alternator) are like buckets of water. Imagine 3 indentical bucket of water, each filled to a different height with water. Pretend that 12 inches of water is 12 vDC. A battery has 12 inches of water, A charger or alternator, when turned on, have 13 inches of water. Connect all three together and then connect to a spigot. The buckets will always try to level out. The buckets with 13 inches will try to flow into the 12 inch bucket (battery) AND out the spigot (to the lights, or a fan). Turn off the spigot and all the 13 inches will try to go to the battery until it gets to 13 inches also.(This does NOT work for alternating current).
If you turn off the alternator (disconnect the tow or turn off the charger) then the battery is now the deepest bucket and all the water to the spigot will come from the battery. It's all automatic by itself. The tow vehicle's positive wire usually just connects to the fuse panel at the same place that the trailer battery positive wire connects. Same thing for the negative wire.
Some tow vehicles have one way valves (diodes and relays) to make sure water won't flow the wrong way, back from the trailer charger into the tow vehicle. Some don't. If your vehicle didn't come already wired this way, the ultimate one way valve is to disconnect the trailer from the tow. Pull the plug when you stop. Put a little tag by the speedometer or ignition key to remind you to reconnect before you drive away.
As for the battery on the tongue. I have no problem with that. Marine boxes are a good start. It's not essential that the box be weather proof. I might be sure there are one or two weep holes in the bottom if driving rain entered the box.