bass traps . Which kind

GIK Acoustics or Real Traps are both great people to deal with and will assist with your issues/problems/questions.

SuperChunk will work a little better than air behind. Ethan has stated this many times.

Another solution to cover more area is, instead of straddling the corner, have two 4" panels on each side wall going away from corner.

I do not want to bother companies i have no intention of purchasing goods from . I want assurance the last statement about the straddling corners will outperform the superchunk. If it does i will have a ton of extra material for ceiling and more wall panels.
The supercunk method uses say, ten times more material than ethan weiners way

If your speakers are set up properly and assuming you have a somewhat normal room there is absolutely no need for any room treatment.
Normal furnishings drapes, etc, do a remarkable job of letting the sound decay in a natural way.

If the speakers are not set up to act "as one" no amount of room treatment will ever get you where you want to be.

well, when you treat a room you treat it for acoustical pressure (bass) &/or for acoustical waves (mid/highs). When you are treating the acoustical waves you'll find that the treatment is rarely slammed against the wall - there's almost always an air gap. That's because when the acoustical wave hits the wall it stops. Thus, No use having the acoustical wave treatment against the wall when the wave has already stopped!
when you are treating bass the treatment is often in the corner 'cuz bass waves reinforce in the corner. Bass traps are almost always slammed against the wall. And, since you are treating acoustical pressure you need to have suitable material inside the treatment that absorbs bass freq (20-400Hz). The burlap outside is just for cosmetic purposes. I've also found that you need a lot of material to absorb bass effectively as opposed to a 2" or 4" panel to absorb mids/highs.
Not sure why the Real Traps work better for bass absorption with air behind them?? does not make too much sense to me. Maybe they are trying to absorb lower mid freq as well?

Sound doc, while room furnishings can go a long way towards ameliorating problems, they only affect the higher frequencies. Few of us have such perfect listening rooms that there are no low frequency anomalies. Many rooms have 10-20db. peaks or valleys in their response and it does take either room treatment or equalization to address these kinds of problems. Plus, many don't have the luxury of locating their speakers so that first reflection points don't create imaging problems. If you've got a mid-century room design with stone, tile, or wood flooring, large expanses of glass, and minimal curtains, you're are likely going to need some acoustic treatment IMO.