...purchase a generator for my Prime Time 3150 BHS...
The trailer you have probably has at least 13,500 BTU HVAC. However, a number of trailers are coming equipped with 15,000s. You should determine which one you have.
...Was once told that I would need a 3000i (from Honda or such), but was hoping I could get away with a 2000i which is at Costco for $450 or so. I also know that you can "pair" this with another one for more power...
If you have a 13,500 you might get away with something like the Yamaha 2400IS. It will run the 13.5 pretty much reliably below 6,500 feet even on a 100degF day based on my personal experience.
My previous trailer was a Trailmanor and the Yamaha would definitely run the AC plant, TV, lights but forget the coffee pot or hair dryer. Either one of the latter is pretty close to kilowatt load EACH by themselves.
I never tried running the 13.5K on a 2000, and it might do it when conditions are right. But reliable it won't be as you are too close to max current load on the 2000s when the air conditioner's compressor starts up.
The new trailer has 15K AC, and a 2000 absolutely will not run the AC plant. I am using the dual Hondas, but I have seen people using the Honda/Yamaha/Boleys 3000s and never saw them have problems.
There are a number of options on gensets, but they basically fall into two categories: inverter and contractor(non-inverter).
Inverter types have a direct current generator connected to a quality dc to ac inverter. The addition of the control system and some good engineering, yields a genset that is both quiet and has exceptionally pure AC.
Contractor type are the rather conventional small engine powered generators that have been around for decades. Their prices have plummetted and a reasonably reliable 4KW genset can be had for around $400.
The downside for these are that they a spartan to say the least. That is one of the reasons they can be had so cheaply. They do not control amplitude or frequency very well, but they were made for utility and not to power mission critical applications.
This breed is also hard to make quiet too. Noise suppression in genset is more than just putting a muffler on the exhaust. There are plenty of other parts making significant amounts of noise that need to be silenced too. If you inspect a super quiet, you will see that engine is engineered to be quieter and care has been taken to keep the noise from radiating beyond the case.
All that engineering and technology costs money. A super quiet is not just a lawn mower engine in a fancy box.
The other thing to note about all generators is the decibel rating. Decibels are in logarithmic units
instead of linear. So just a few decibels difference in noise could be 10 times as loud.
To determine what you need you should put together a power budget. What you do is make a list of everything you want to run and add the watts it takes to run those items. That is your power budget. One thing you should realize is that not all of those items will be pulling maximum draw all the time. If you stagger when you run certain items you won't over load the genset very often.
Another concept to grasp is that inverter type gensets deliver quality power. That is not a dig at the contract types, but because inverter types deliver power at the correct amplitude and frequency, devices run more efficiently on them.
Contractor type have to ramp engine rpms up and down to meet load demands. These rpm changes causes variations in the frequency and amplitude of the power. This can cause devices to run less than optimally. Frequently, you will need a larger genset to handle the load better. I have had appliances that on paper should run on a on something as small as 2KW contractor type, but would not. If I hooked up the same appliance on 2KW inverter type they ran all day without a hitch.
Even so, a contractor type that would power your trailer would cost considerably less than the inverter style. Still a 4KW contractor type that would probably run most of your trailer and 13.5 HVAC is only going to cost a shade over $400. If a Yamaha 2400 would work for you, those start around $1,200 and more powerful gensets more than that.
If noise is not a problem, either for you or your neighbors, a contractor type is a good way to go. That is to say that even if the contractor type does not hold up well (I personally think if they are maintained they will run just fine) you could buy 2 more for the money you save not buying a Yamaha 2400is.
Options for your genset are something else to consider too. Most of the 2KW types, inverter or contractor, lack remote start. People that have purchased the larger gensets with remote start will attach their genset to the rear of their RV on some kind of exterior storage shelf.
By setting up like that, they leave their air conditioner on in the trailer with the genset off. When they are a half hour away from a stop, they will remote start the genset from the cab of the TV, the air conditioner comes to life cooling down the trailer just in time for a lunch or pit stop. Of course these remote features are also nice since you do not have to get dressed to start or stop your genset either.
The advantage of the daisy chainable 2KWs types are on those days when you don't need to run your air conditioner. When you don't need the extra capacity you just run one. Also it gives you the additional capability of using one genset in one location while have the other being used elsewhere. The other advantage is that 2KWs are more man portable. The Yamaha 2400 is about as heavy as any one person should try to move.
The only other thing to discuss are extended run tanks. Short story, Hondas handle that well (because they have a fuel pump). If the genset you pick has a fuel pump, it will likely handle external fuel tanks well.
Hope this helps...