Well, four 18mm canted motors won out over one 29mm. I had hoped for an actual mathematically generated template to cut out the motor holes but in the end just started chopping. Heres a pic of the first two motor tubes drying. Some additional filling will have to be done but the results should be satisfactory. Satisfactory enough for a cardstock-topped, goonie oddroc!
I have two fin material choices based on what I have on-hand. Either some high quality 1/4" balsa or some corrugated plastic. I'm leaning towards the latter because it just seems to fit with the general construction of the rocket. Prepping a mailing tube rocket with huge corrugated plastic fins that are held on with - gasp - hot glue just reinforced this feeling. Plus I just don't feel like papering fins. I'll see.