Jeff
Not sure if my experience is the same or helps but I dont have your added cerebral palsy problem to deal with.
I had a ileostomy 2 months ago and had 4 nights is row recenly where my bag leaked. Perhaps due to the shape of my body but also I think this was due to moving around when asleep. I was given a different sort of bag that can have a belt attached. The seal is also different on this model.
I found this helped at night. The second thing I have tried is a belly band to hold the bag close. This is actually commonly warm my females and sold as a belly band or boob tube The ones I purchased are longer than normal, just plan so not really neccessarly a female type clothing item as such . I have a couple about 48cm high, made of a soft cottom elastine material so can easily stretch as the bag fills, but helps to keep it close. It is also useful to cover the bag, is case there is gap between pants and shirt.
the bag Product number 14418 Coloplast, Alterna, one piece bag.
I am in New Zealand, so we have a ostomy nurse visit twice a week, and they have specialist knowledge in deal and solving problems.
Cheers and good luck
Gary