You know, Wayne, that's exactly what we ran in to with the salesman that we talked to.
I didn't expect a salesman to ever try to talk us out of anything. I assumed that his comission would go up as the price of the rig goes up. Also, we have used the shrink wrap film on single pane windows in a home that we once owned and they did work well, however, they were fixed panes of glass that didn't open and I wouldn't want to mess with taking it off and re-installing just to open the window.
I believe we are going to go ahead and add the dual pane windows to the rig so that they can be installed at the factory. I think that would be better for the integrity of the rig as opposed to having someone install them at a later date. Besides, if I had a nickle for every time we said "we can do that later" and never did, I'd have enough to pay for the windows