Acetone works the best for small cracks,,actually, acetone works with the larger cracks but ABS sheet stock
should be used to "back-up" any major seperation.
Acetone should be used thru a syringe and don't allow the solvent to "puddle" anywhere inside the hull or
it will try to melt it's way outa the hull. Try to find some hobby sheet styrine for patch and doubling repairs.