It is possible to specify a custom PulseAudio startup script using the default-script-file config parameter. So another option without autostart.sh would be:
default-script-file = /storage/.config/pulse-daemon.conf.d/custom.pa
#!/usr/bin/pulseaudio -nF
.fail
.include /etc/pulse/default.pa
# extend default startup script
load-module module-rtp-recv latency_msec=250 sap_address=0.0.0.0