I fashioned a mount for the timer from the plastic cover from a pack of Estes motors. It fit nicely short-ways across the section that holds the igniters and plugs. Some snipping, folding and duct tape formed a holder which has mounting flanges on three sides. Holes were cut for the knob and the cable-tie trigger.
I drilled a hole in the tire valve cap and made a pin from a paper clip. The one lingering issue is that the knob on the winding shaft is thin and is not solid across its face. The cap is not very tight and very well might fall off during boost and has a 100% chance of loss on ejection.