custom profile:

"oneboxx": {
		"profile": "gl-e750",
		"version": "3.027",
		"imagebuilder": "3.1/openwrt-imagebuilder-ar71xx-generic_3.1",
		"packages": "gl-base-files-ar $basic $custom_oneboxx $storage $usb $glinet gl-e750-mcu gl-ble-daemon gl-ble-api"
	},

where:

"custom_oneboxx": "iptables-mod-ipsec kmod-crypto-authenc kmod-crypto-cbc kmod-crypto-ctr kmod-crypto-deflate kmod-crypto-des kmod-crypto-ecdh kmod-crypto-echainiv kmod-crypto-gcm kmod-crypto-gf128 kmod-crypto-ghash kmod-crypto-hmac kmod-crypto-iv kmod-crypto-kpp kmod-crypto-md5 kmod-crypto-rng kmod-crypto-seqiv kmod-crypto-sha256 kmod-crypto-wq kmod-ipsec kmod-ipsec4 kmod-ipsec6 kmod-ipt-ipsec kmod-iptunnel4 kmod-iptunnel6 kmod-lib-zlib-deflate kmod-lib-zlib-inflate libaio libatomic libiwinfo-lua liblua liblucihttp-lua liblucihttp liblzma libmariadbclient libncurses libstdcpp libubus-lua lua luci-app-firewall luci-base luci-lib-ip luci-lib-jsonc luci-lib-nixio luci-mod-admin-full luci-proto-ipv6 luci-proto-ppp luci-theme-bootstrap luci mariadb-client mariadb-server nano nginx openssh-sftp-server php7-cli php7-fpm php7-mod-curl php7-mod-hash php7-mod-iconv php7-mod-json php7-mod-opcache php7-mod-openssl php7-mod-pdo-mysql php7-mod-pdo php7-mod-phar php7-mod-session php7-mod-shmop php7-mod-simplexml php7-mod-zip php7 rpcd-mod-rrdns rpcd strongswan-charon strongswan-default strongswan-ipsec strongswan-libtls strongswan-mod-aes strongswan-mod-attr strongswan-mod-ccm strongswan-mod-cmac strongswan-mod-connmark strongswan-mod-constraints strongswan-mod-curl strongswan-mod-curve25519 strongswan-mod-des strongswan-mod-dnskey strongswan-mod-eap-identity strongswan-mod-eap-md5 strongswan-mod-eap-mschapv2 strongswan-mod-eap-tls strongswan-mod-fips-prf strongswan-mod-gcm strongswan-mod-gmp strongswan-mod-hmac strongswan-mod-kernel-netlink strongswan-mod-md4 strongswan-mod-md5 strongswan-mod-nonce strongswan-mod-openssl strongswan-mod-pem strongswan-mod-pgp strongswan-mod-pkcs1 strongswan-mod-pubkey strongswan-mod-random strongswan-mod-rc2 strongswan-mod-resolve strongswan-mod-revocation strongswan-mod-sha1 strongswan-mod-sha2 strongswan-mod-socket-default strongswan-mod-sshkey strongswan-mod-stroke strongswan-mod-updown strongswan-mod-x509 strongswan-mod-xauth-generic strongswan-mod-xcbc strongswan terminfo uhttpd-mod-ubus uhttpd zoneinfo-africa zoneinfo-asia zoneinfo-atlantic zoneinfo-australia-nz zoneinfo-core zoneinfo-europe zoneinfo-india zoneinfo-northamerica zoneinfo-pacific zoneinfo-poles zoneinfo-simple zoneinfo-southamerica"

built using:

./gl_image -c customize.json -p oneboxx

gives error:

openwrt-oneboxx-ar71xx-generic-gl-e750-squashfs-sysupgrade.bin is too big