I'm sure you could create an enclosed, gas powered pedal tricycle with load capacity and long range, but it seems like a really odd way to go about it since it'll cost a fortune and be worse that off the shelf options in every way.
The frame and components won't be up to all of the additional weight, you 'd need to pretty re-build the whole thing.
If you're scared of traffic, then trying to ride in traffic in a top heavy, unstable trike is going to be terrifying.
Personally, I'd either try and get over the car phobia (and logically it's safer being *in* one than on a bike *outside* one) or just spend the money on Uber or buses.