This weekend while rehearsing we had an unexpected and unplanned visit from the prince of darkness.

We could continue ala acoustic but without a bass. I then hit upon an idea to build my own acoustic bass but something unique from parts already in my possession or easily and cheaply sourced.

Sound box - Galvanised wash tub
String length 25.5" as i do not know the standard settings for a bass and I am afraid that the fretting may be incorrect.
Neck, a recovered First Act neck of an otherwise useless guitar
Pick ups from same useless guitar to be used during the presence of light or as a novelty with the instrument.
Hard woods from the local timber supplier, some coach screws, bolts, nuts odds and sods

I have drawn a rough sketch which I will publish once scanned.

However strings will be limited to A,D,G only as I think that there may be tension issues. The functioning of the pick ups are debatable with these heavy strings.
The question is what gauge would be suitable for such a short length wash tub bass?
Is it viable to do such a modification without having to resort to serious moola for a decent acoustic bass?

Guidance, corrections assistance will be appreciated.

Thanks