Check the propane fire thread. I tested my CFIAC and 5 lb tank and posted results. On full throttle I got 3-5 hours (can't remember exactly). If space is not a constraint I'd probably lean towards the 10 lb, though.
Looks like 10lb/11lb gas tanks come in two styles: Short and fat or tall and skinny. I think the tall/skinny model would fit better on the tongue of our trailer:
We could probably put a bracket on the tongue just in front of the tongue box and as long as we were still able to open the tongue box, we'd be OK.
I like my 5 lb tank. Like someone else said, the initial price is tough to swallow. But for capacity, size, and price-to-fill it's the right tank for me. You can modify a fire extinguisher bracket inexpensively to mount one on a vehicle or trailer:
Any info on the source for that Extinguisher bracket? I finally have a place to mount my 5lb tank but can't spare the cash for the beautiful aluminum bracket from Adventure Trailers...
I just went to the local fire suppression dealer, gave them the tank diameter, then cut the height down at home. You should be able to do the same. Great way to save a few bucks.