For 1/5 scale Galeb G2 you can optionally buy tip tanks.

Tip tanks are made on vacuum machine from 0,5 mm white styrene plastic. Few 5 mm balsa rings and parts included in this set...

Tip tanks are 60 cm (23,6") long.

How to install tip tanks check here:

Ribs will have washout for better stability on slow speed. Tip tanks will just increase that stability.