You might try G-flex by west systems, more viscous than accraglass but flows better with some heat. Strong and as the name implies, it has a fair bit of flex to it. Designed for wooden boat repairs, good stuff.
Excellent product and works exactly as described by the company. You can buy it with differing speeds of hardening agent. My son and I bought a gallon with the extra slow hardener for a boat project. It poured well and filled cavities, and was strong enough to hold the bolts for the motor mounts on the 350 ci. V-8.
https://www.westmarine.com/resin-resin-hardener
