I am doing a rip and replace on a very low slope (2 in / 10 ft) roof. Four + decades of DIY experience and three re-roofs (but they were all shingles on pitched roofs). This will be my first rolled roofing project (other than a couple of sheds). The project is 2,200 square feet, so cost is a concern. I really like everything I have read and heard about the self-adhesive (peal and stick) products. They seem to be made-to-order for the DIYer. The peal and stick top sheets (mineral surface) cost about twice as much as the regular top sheets. But the savings on adhesive and labor would appear to be well worth the extra cost. But I have questions about the underlayment. I see both two layer (underlay + top sheet) and three layer (underlay + intermediate ply + top sheet) approaches. However no discussions about when one is more appropriate than the other. I also see self-adhesive underlayment, but they are expensive (about five times the price of 30# felt) and will add $800 to the project. Im not really keen on gluing the underlayment to the plywood sheeting (AKA peal and stick underlayment). I cant give a good reason other than the difficulty that will cause in a re-roof 20 years from now. What I am proposing is to use 30# felt underlayment (one layer, not two). Stapled at the top edge because I believe I will have fewer problems with pop ups using staples than I would with nails. Lapped four inches (rather than the usual 2 inches) and sealed with Henry #203. Then finish with a GAF (Liberty) peal and stick 90# mineral surface top sheet. I live in the desert of Arizona, so I dont have to worry about the special edge treatments for ice damming. Comments and advice will be much appreciated. Particularly with respect to the underlayment.