What kind of generator for a 1978 Wilderness trailer

http://rvservices.koa.com/rvinformation/rvmaintenance/basic-rv-electricity.asp

This site here, has basic rv info.
You could try to contact distributor for your rv, see if they can help with owners manual.
You can do a web search for your owners manual, see if anything comes up?

honda make good generators
a service should sort it out
motor part
generator has a govenor that can be adjusted
check carby idle .bad fuel . ,coil lead and plug
four stroke may need valve adjustment

generator part
check its voltage output and how much load you have on it when it has the rough idle

The link below will give you lead to a supplier. I don;t know anyone at this dealer but hopefully you will get the parts you need.

Dometic HZB 15S Portable Ice Maker 120 Volt RV Parts

Before you get too carried away, are you aware that no matter what size inverter you are running, you need enough battery capacity to convert to AC (hydro) . 1 x 100 amp battery will not last very long under that load. Do you have plans, or storage space for a few more batteries? How/what are your plans for charging those batteries after usage, such as plugging the trailer in or an external charger, or perhaps solar panels?All that needs to be considered. Look at appliances you plan on running and get the watts, or amps required reading of tags, then it will be easier to calculate for you, and recommend possible solutions.

You do not want to convert anything to a 220 v connection !!!! Your RV is 12 volt DC and 120 volt AC.
Use a 30amp female to 15 amp male adapter to plug in to regular household receptacle on generator. Available at hardware store and RV stores.

Because it won't be powering just your AC, I would recommend 5000W. It's that big amp draw when compressor kicks in that will pull it way down, if not strong enough. Take for example the fact that a dedicated 20 amp breaker and cable are the norm for RV's to use for AC now. Double check also that the generator your purchasing will take a momentary surge draw of up to 20+ amps without tripping breaker on generator. I say 20+ because once RV is plugged in or wired to generator, it will be powering any other hydro operated appliances, lights, converter etc that the trailer has on board. I bought a cheapie rated at 4000W, and 3000 running watts, but it kicks out the breaker just trying to start my portable air compressor, rated at 15 amps.

RV water lines can sometimes be difficult to locate. But typically, by removing a panel or an accessible flooring section, Youcan successfully gain access to most of the fresh water plumbing system. The clue to a removable panel is to look for screws instead of staples holding them in place

I had a similar problem on my 1995 Holliday Rambler Aluminalite 29 foot travel trailer with the similar layout of your trailer. My converter was only putting out 12.28 Volts DC. I fount the converter under the front of the trailer. (facing the front of the trailer, just right of center about 8" back)
There was a pannel with screws on the underbelly. I could hear the humm of the transformer. I removed the cover and found the red wire from the converter to a stud nut was loose. Tightened the nut and now I have 13.29 Volts DC.

Regards.