modifying the rear of the frame

[pengyou]

It is feasible/advisable to replace the rear part of the frame of my beach bike so that it is about 6"longer and can accommodate a hub motor (which means making the frame wider) plus a cassette of 4 or 5 gears? I also want to have space between the seat post and wheel to store a battery set, ideally two battery sets up front, one in the middle and one in the back to provide a more favorable weight distribution. The longer frame is also to be able to accommodate more "stuff" and smooth out the ride over some of the potholes, rifts, dings, cracks and crevices that I encounter every day. I know that a longer wheelbase is not as maneuverable in the city but I am willing to sacrifice that for smoothness. My goal...dream...is to be able to go 100 miles on a charge with no pedaling - and maybe 130-150 with pedaling. Yes...dream...and save up lots of pennies for lithium batteries :)

[Peterpan1]

You can put anything you want back there. Look at the Big Dummy frame by Surly, in fact look at the original extracycle which acheives some of this with a bolt on.