G4 Pond Seal for a tank

[blowupcavs]

i have been looking at building a huge 9x4x4 with a 80"x40"x0.5" plexiglass window in it.i have had problem building my large tropical vats so i dont want to use fiberglass. but G4 Pond Seal as i here it can just be painted strait on to brick and concrete but will it work with smooth plywood and MDF.can people let me know.thanks