Here is a pic of the front setup. These are actually water bottles, but the holders are the best I have found. They usually run under $3 each.
The rubber band is a 3/4" slice of an old 4" MC tube. I made a bunch of them.
As far as fuel pressure being a problem, I don't see any issue. The little red plastic cans you buy to fill your lawnmower are NOT vented. I have strapped one of those on the back of a bike in the old days, and you just have to remember to open the cap slowly. Same problem if it gets hot out. The gas you put in is usually from a cold underground tank, and will expand as it warms up.
I leave about an inch of air at the top of the can and all seems to work fine.