On the agenda too (stretch and offset double springs - got the idea from you as well ;) ). Maybe this is too much though and i only double spring the struts. My reasoning is that dual springs probably retain the added spring force longer than a stretched single spring. But feel free to educate me ;)
I have only double sprung my own box and my box has the square section springs. They have been in there since 1999 and I have never not had them in there, so I cannot actually tell you how much better, if better at all, it works.
In my understanding of springs, they can only loose tension if they get overheated or over stressed, or fatigued. I don't think either situation can arise after these are installed.
