Support SnS is fun! This is my SnS support build. It's not optimised so it can still be improved. An alternative to Grand Barong II would be Malady's Tabar III (lower paralysis damage and no deco slots).
Weapon:
Grand Barong II
Armour
Wiggler Head A
Dober Mail B (Can be changed)
Dober Vambraces B
Bazel Coil B
Kirin Leg Guards B
Earplugs Charm III
Skills Activated
Wide-Range 5
Earplugs 5
Free Element/Ammo Up 3
Speed Eating 3
Attack Boost 2
Mushroomancer 2
Stamina Surge 1
Flinch Free 1
Wide-Range 5 is the core of this build. Most consumable items work with Wide-Range so you'll have to prepare sufficient supplies in your pouch. Speed Eating 3 is also a quick and safe way to use your items. Moreover, if you lack items like Demondrug and potions, Mushroomancer 2 enables you to consume mushrooms for similar buffs.
Earplugs 5 gives me 2-5 seconds to buff/heal my teammates when monsters roar (which is quite often), you could even plant traps to immobilise the monster during this period. Finally, Flinch Free is important in multiplayer quests, especially with randoms.
Grand Barong II has a hidden paralysis element and that requires Free Element/Ammo Up 3. Paralysis is amazing as it creates openings for more team DPS, healing, re-positioning etc.