Tri-bars/Aerobars on Mountain Bikes I am trying to work on endurance in the hopes of one day touring the GDMBR in a reasonable amount of time and after watching Ride the Divide, I noticed a lot of the riders are using aerobars. When I am training, I can ride close to 40 miles on my bike with a Specialized flat bar but I am noticing significant pain in my back, tailbone, wrists and shoulders.
Are aerobars the answer to my pain problems? My assumption (from purely a comfort viewpoint) is that aerobars allow you to shift your weight occasionally and distribute your weight differently without stopping. If so, is there a certain type of handlebar I should be looking at for a mountain bike? I would prefer an easy to install/uninstall solution because I am not always looking to have these handlebars on. Also, is adding an aerobar the proper solution or am I looking at it wrong? I am questioning bikes at the moment and would be grateful on any tips.
I have never used any other type of handlebar other than a flat bar, so please include anything that may seem incredibly obvious.
Note: I looked at this answer but those look incredibly uncomfortable for long distances and seem pointless for what I am doing.

Specifications
Bike
Specialized Myka Sport 29er
Handle Bar Specs
Specialized flat bar, alloy, 640mm &amp; 660mm wide, 8-degree backsweep, 4-degree upsweep, 25.4mm
Full Specifications
The main reason that aerobars may have an advantage over flat or road bars is that they are designed so that your main support mechanism is skeletal, rather than muscular. The longer the distance, the more this will hold true.



This picture is of a top triathlete. Note that the forearms are almost parallel, and the upper arms are at a 90 degree angle. This allows the main support for the upper body to rest on the bone structure, with minimal muscle involvement. (Stadler was an Ironman distance triathlete, bike segment of 112 miles). 

While you may see variations on this, it is a general truism that the longer the race, the more comfort trumps aerodynamics, and vice versa (Short races aerodynamics trumps comfort.)

Many of the ultra mountain bike competitors set up their rides similarly, and have "wrap" style aerobars that allow them multiple different hand positions for control, as well as the resting position where their arm muscles don't have to do the work for support.

That all being said, I would point out that many riders go much further than 40 miles with no pain at all. This would suggest to me that your fit is not correct, or that you are not in shape enough for a 40 mile ride yet. Tailbone pain is (usually) a bad saddle and fit, and the rest is also easily attributable to fit. Aerobars will not be a magic cureall for an improperly fitted bike