Power Inverter

I just got my power inverter and I am trying to figure out what I need to install this.  I have a 800/1600 Watt unit that has 3ft 8 gauge wire with jumper cable clips on one end. I want to wire it directly to the battery, but the wire is not long enough to do so where I want it.  So I read the manual and it says to use 4 gauge wire when you want to make the wire longer then what is supplied.  Is this necessary to use 4 gauge when all i want do is go from 3 ft to about 4 ft of wire?  I just figured that since it came with 8 gauge that would probably be OK since I am only going to make it a foot longer. 

Here is another:  I have a 110 Pigtail that I bought, and i was wondering if could just plug this into the inverter and then hook up the wires to a household electrical outlet? I dont see why not, but I just wanted to make sure that the pigtail was ok for this purpose. 

Also if anyone has any ideas that they could suggest I would appreciate it.

Thanks for reading

There are four 25 Amp Fuses (Spade Type).  Now that I am going to extend the wires from the switch on the inverter to an accessible spot on the dash, I will not need to use more than 4 feet of wire for sure, and I am hoping that the 8 gauge wire that came with it will be long enough.  I might just get 4 gauge anyway since I do not need much, and now I will have no trouble connecting such a large ring terminal since I can connect it directly to the battery and directly to the inverter ( before I had planned on running the power through a household switch until i read how I could just use the switch on the inverter and just extend the wires like i mentioned above). 

It is possible that I would run this at its max load, however it is not likely I would do so often.

Thanks

I would honestly use the 4 ga wire for this application...8ga might be sufficient, but just in case, you dont want to be limited by wire size...

be sure to mount the inverter INSIDE the cab, and not make the mistake that I just read about and mount it under your hood...

I am planning on putting under the dash and using a pigtail to plug inot the inverter and run it to a switch of some sort somewhere al ittle more accessible.  I didn't like the idea of puting it in the engine compartment just like you said.  Do you have any advice on this idea of using a household switch wired from a pigtail.  I guess i couls just use a regular extension cord, but I sort of like the idea of having an outlet somewhere that I can plug in and out easily without having to deal with a loose cord that I would have to keep hidden so it wouldn't look ugly.  Are there any other solutions for a remote receptacle?   I am putting it into a MiniVan so I do not want it to be in an obvious place, but I want it accessible and not an eye sore.  I was looking into the amount of wire I will need and I think I will be able to get away with the 3ft sections of 8 gauge that came with it if i just cut off the clips, would you still advise 4 gauge even though 8 gauge is what came with it.  It is a 800/1500 watt unit. 

Thanks a lot for your help