Go the 6" poly tube, built mine a while back and runs damn awesome, now that I have worked out this you tube thing I will be putting the build up for all to see.
Works great, reasonably portable and remember make it as small as possible as you are only shovelling into it.
I ran mine on a 100 amp hr battery and it continously ran for 16 hrs and still had some juice left, quiet as a mouse but you do need a petrol pump to move the water though.
I posted my build here a while back, made out of scrap shits and bits, goes well
Cheers Brad....