Minimum slope for rolled asphalt roof
I don't think what you are proposing will work. Asphalt rolled roofing is NOT waterproof. Sealing at the joints and eave will stop wind blown rain, but standing water will saturate the paper and it will leak. (The paper is not UV resistant either.)

I wouldn't use a "peel and stick" membrane either, like Grace "Ice and Water Shield", because they can only be used on slopes down to 2:12. (...plus they have no UV protection.)

I'd use an PVC membrane. I would not use an EPDM membrane. The main difference is that EPDM's seams are chemically sealed and PVC seams are heat welded together. The EPDM seams can breakdown over time. 

...but back to your question, No, I would not use roll roofing sealed with mastic.