My tank was styrene sheet and evergreen strips - rivets were Archer decals - fiddly but doable. Support was stained stripwood from my US modelling stash. Ladder was a long signal ladder - MSE I think.
Open topped with an insert of clear plastic sprayed Humbrol Olive drab on the underside (same as my canal)
The prototype actually looks pretty big in photos so it is "downsized"