Gas will be more readily available. Gas trucks generally have more payload, gas trucks cost less, gas trucks are more common when you are looking to buy.
Go for a one ton, just a little more cost and a lot more truck. An 8' bed does not necessarily mean a bigger camper..just one that does not hang over the back. I go through some stream crossings where anything hanging over or sticking out in back would be in danger of dragging, so my camper ends where the bed does. I can also tow without the disadvantage of a hitch extension.