bicycletricycle - -
i shoot paper negatives pretty often, but not extended exposures as you write about. the problem you may have with your paper negatives is that paper in inherently more contrasty than film, and you may get all your hi's and lo's all blown out. i usually use older paper because it doesn't have the same problems as brand new paper. you can fog by flashing it ( as you might when enlarging ) and that might help your contrast a little bit. its too bad you can do a test or 2 beforehand. in order to get a good print you probably want to meter @ asa 6, shoot less in bright sun than in overcast conditions + underexpose about 1-1/2 stops ...
good luck with your camera obscura!