It looks like your trike has gears, is that correct?
If so then you might like this setup, I've built 3 like this and kept this last one for a shop bike for parts runs.
cyclone-e-bikes motor with freewheel sprocket mounted to a standard freewheel bottom bracket assembly for sick bike parts as the motor is high enough to not need wider crank arms.
I put the battery, controller and charger in that black metal box in back, then mounted the basket to the top but you could mount a back facing chair just as easy.
The trike pictured has a 6-speed derailleur, it will putt along at 1 MPH and top out at 25MPH on flat pavement, the important part is putt putt along and very low speeds without bogging which would be hard for any gas powered direct drive.
The motor, controller and bottom bracket are about $400, the expensive part is the battery.
I have a $600 overkill battery for your needs in mine but at the speeds and distance you will be riding even in the Nevada desert I'd bet it would last you the whole week without a charge.
My server is down today so the pics don't display today but the parts specs are in this topic here
http://motorbicycling.com/showthread.php?t=44144
Regardless of the motor choice you make you really should flip the trike over, clean and lube the wheels and check the drive train, it looks pretty 'rustic' if you know what I mean ;-}
Good luck with the project and drop me an E if you have questions about the parts.
