Not sure what you mean--a "runaround track" is a siding where a locomotive can run around cars in order to get on the other side of the train, whereas a "reverse loop" is shaped like a balloon (on the prototype they are sometimes called a "balloon track") where a train enters on one leg, goes around the loop and leaves the loop traveling in the other direction.
30" is too narrow for a reverse loop in HO, unless you are willing to limit yourself to the smallest of locomotives and equipment--the smallest standard curve made in HO is 15", and that 15" radius measurement means the center of the track--which means if you put a half-circle of 15" radius track on a 30" wide table, half of the track would hang over the edge of the layout--no good at all!
Just to show what can be done in six feet, here is half of my layout--it is made up of two modules, one of which is 1'x6' and the other is an L-shaped piece 3'x6' in total size:
Here's the same layout from the other end:
I noticed in another thread that you want to build two 30"x72" modules--do you want to attach them end to end, to make a 30"x12' layout, or back to back, to make a 5'x6' layout? If the latter, you could give each module a C-shaped track plan and include a backdrop in the middle. If you're still thinking of a logging layout, you could put the logging camp on one side, with a branch line going up a steep hill to actually reach the logging camp area, and the lumber mill on the other side. By putting a backdrop in the middle, you create the illusion that the two points are actually very distant from each other. Mountains help, but you might not have enough room to build a mountain too tall to see over--a backdrop lets you put two-dimensional mountains in back of your 3-D plaster mountains, creating much more of a mountain scene.
