Just about every Tiger is different from every other Tiger, even when they look the same from the outside. Take a look at the website under Tiger Models to see what is currently being built.
http://www.tigervehicles.com/My Tiger, a 2006, is built on a regular-cab chassis and is under 20 feet long. Nothing that size has a "lot" of room, but I know couples who full-time in them and are not midgets. The bathroom is a wet bath type, large enough that not many Tiger owners complain. As to the bunk, I'm older and have bad knees and I sleep downstairs on the foldout bed.
Gas mileage varies; I got almost 14 on the open highway on last week's trip. However, some Tigers are gas and some are diesel. Some have a larger heavier chassis and more weight both inside and out. Slow travel on rough roads eats up fuel.
My Tiger does not have solar or a generator. I do fine with about 220 amp hours of AGM batteries in the coach; they recharge from the engine when I drive.
You can mine the Tiger website for info. If that is not enough, PM me and I'll try to help.
One more thing: the Tiger is NOT a truck camper, it is a Class C. I just hang out on the TC forum because I like it and do TC sorts of things.